diff --git a/src/gn/compile_commands_writer.cc b/src/gn/compile_commands_writer.cc
index 9f8ef63..1d9d5b4 100644
--- a/src/gn/compile_commands_writer.cc
+++ b/src/gn/compile_commands_writer.cc
@@ -15,7 +15,6 @@
 #include "gn/config_values_extractors.h"
 #include "gn/deps_iterator.h"
 #include "gn/escape.h"
-#include "gn/filesystem_utils.h"
 #include "gn/ninja_target_command_util.h"
 #include "gn/path_output.h"
 #include "gn/string_output_buffer.h"
@@ -324,11 +323,7 @@
     OutputJSON(build_settings, preserved_targets, output_to_json);
   }
 
-  if (!json.ContentsEqual(output_path)) {
-    if (!json.WriteToFile(output_path, err))
-      return false;
-  }
-  return true;
+  return json.WriteToFileIfChanged(output_path, err);
 }
 
 std::vector<const Target*> CompileCommandsWriter::FilterTargets(
diff --git a/src/gn/filesystem_utils.cc b/src/gn/filesystem_utils.cc
index 4906d56..6471378 100644
--- a/src/gn/filesystem_utils.cc
+++ b/src/gn/filesystem_utils.cc
@@ -939,15 +939,6 @@
   return file_data == data;
 }
 
-bool WriteFileIfChanged(const base::FilePath& file_path,
-                        const std::string& data,
-                        Err* err) {
-  if (ContentsEqual(file_path, data))
-    return true;
-
-  return WriteFile(file_path, data, err);
-}
-
 bool WriteFile(const base::FilePath& file_path,
                const std::string& data,
                Err* err) {
diff --git a/src/gn/filesystem_utils.h b/src/gn/filesystem_utils.h
index 9f21cff..2c826b5 100644
--- a/src/gn/filesystem_utils.h
+++ b/src/gn/filesystem_utils.h
@@ -203,14 +203,6 @@
 // otherwise.
 bool ContentsEqual(const base::FilePath& file_path, const std::string& data);
 
-// Writes given stream contents to the given file if it differs from existing
-// file contents. Returns true if new contents was successfully written or
-// existing file contents doesn't need updating, false on write error. |err| is
-// set on write error if not nullptr.
-bool WriteFileIfChanged(const base::FilePath& file_path,
-                        const std::string& data,
-                        Err* err);
-
 // Writes given stream contents to the given file. Returns true if data was
 // successfully written, false otherwise. |err| is set on error if not nullptr.
 bool WriteFile(const base::FilePath& file_path,
diff --git a/src/gn/filesystem_utils_unittest.cc b/src/gn/filesystem_utils_unittest.cc
index 347d0fe..0eb786d 100644
--- a/src/gn/filesystem_utils_unittest.cc
+++ b/src/gn/filesystem_utils_unittest.cc
@@ -638,43 +638,6 @@
   EXPECT_FALSE(ContentsEqual(file_path, "bar"));
 }
 
-TEST(FilesystemUtils, WriteFileIfChanged) {
-  base::ScopedTempDir temp_dir;
-  ASSERT_TRUE(temp_dir.CreateUniqueTempDir());
-
-  std::string data = "foo";
-
-  // Write if file doesn't exist. Create also directory.
-  base::FilePath file_path =
-      temp_dir.GetPath().AppendASCII("bar").AppendASCII("foo.txt");
-  EXPECT_TRUE(WriteFileIfChanged(file_path, data, nullptr));
-
-  base::File::Info file_info;
-  ASSERT_TRUE(base::GetFileInfo(file_path, &file_info));
-  Ticks last_modified = file_info.last_modified;
-
-  {
-    using namespace std::chrono_literals;
-#if defined(OS_MACOSX)
-    // Modification times are in seconds in HFS on Mac.
-    std::this_thread::sleep_for(1s);
-#else
-    std::this_thread::sleep_for(1ms);
-#endif
-  }
-
-  // Don't write if contents is the same.
-  EXPECT_TRUE(WriteFileIfChanged(file_path, data, nullptr));
-  ASSERT_TRUE(base::GetFileInfo(file_path, &file_info));
-  EXPECT_EQ(last_modified, file_info.last_modified);
-
-  // Write if contents changed.
-  EXPECT_TRUE(WriteFileIfChanged(file_path, "bar", nullptr));
-  std::string file_data;
-  ASSERT_TRUE(base::ReadFileToString(file_path, &file_data));
-  EXPECT_EQ("bar", file_data);
-}
-
 TEST(FilesystemUtils, GetToolchainDirs) {
   BuildSettings build_settings;
   build_settings.SetBuildDir(SourceDir("//out/Debug/"));
diff --git a/src/gn/function_write_file.cc b/src/gn/function_write_file.cc
index 2c568c0..b0884da 100644
--- a/src/gn/function_write_file.cc
+++ b/src/gn/function_write_file.cc
@@ -8,6 +8,7 @@
 #include "base/strings/string_split.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
+#include "gn/build_settings.h"
 #include "gn/err.h"
 #include "gn/filesystem_utils.h"
 #include "gn/functions.h"
@@ -15,6 +16,7 @@
 #include "gn/output_conversion.h"
 #include "gn/parse_tree.h"
 #include "gn/scheduler.h"
+#include "gn/string_output_buffer.h"
 #include "util/build_config.h"
 
 namespace functions {
@@ -87,7 +89,8 @@
     output_conversion = args[2];
 
   // Compute output.
-  std::ostringstream contents;
+  StringOutputBuffer storage;
+  std::ostream contents(&storage);
   ConvertValueToOutput(scope->settings(), args[1], output_conversion, contents,
                        err);
   if (err->has_error())
@@ -97,8 +100,10 @@
       scope->settings()->build_settings()->GetFullPath(source_file);
 
   // Make sure we're not replacing the same contents.
-  if (!WriteFileIfChanged(file_path, contents.str(), err))
+  if (!storage.WriteToFileIfChanged(file_path, err)) {
     *err = Err(function->function(), err->message(), err->help_text());
+    return Value();
+  }
 
   return Value();
 }
diff --git a/src/gn/ninja_generated_file_target_writer.cc b/src/gn/ninja_generated_file_target_writer.cc
index afe1e08..e1ad19f 100644
--- a/src/gn/ninja_generated_file_target_writer.cc
+++ b/src/gn/ninja_generated_file_target_writer.cc
@@ -6,11 +6,11 @@
 
 #include "base/strings/string_util.h"
 #include "gn/deps_iterator.h"
-#include "gn/filesystem_utils.h"
 #include "gn/output_conversion.h"
 #include "gn/output_file.h"
 #include "gn/scheduler.h"
 #include "gn/settings.h"
+#include "gn/string_output_buffer.h"
 #include "gn/string_utils.h"
 #include "gn/target.h"
 #include "gn/trace.h"
@@ -79,7 +79,8 @@
   ScopedTrace trace(TraceItem::TRACE_FILE_WRITE, outputs_as_sources[0].value());
 
   // Compute output.
-  std::ostringstream out;
+  StringOutputBuffer storage;
+  std::ostream out(&storage);
   ConvertValueToOutput(settings_, contents, target_->output_conversion(), out,
                        &err);
 
@@ -88,7 +89,7 @@
     return;
   }
 
-  WriteFileIfChanged(output, out.str(), &err);
+  storage.WriteToFileIfChanged(output, &err);
 
   if (err.has_error()) {
     g_scheduler->FailWithError(err);
diff --git a/src/gn/ninja_target_writer.cc b/src/gn/ninja_target_writer.cc
index c8e7ebd..e85400f 100644
--- a/src/gn/ninja_target_writer.cc
+++ b/src/gn/ninja_target_writer.cc
@@ -23,6 +23,7 @@
 #include "gn/ninja_utils.h"
 #include "gn/output_file.h"
 #include "gn/scheduler.h"
+#include "gn/string_output_buffer.h"
 #include "gn/string_utils.h"
 #include "gn/substitution_writer.h"
 #include "gn/target.h"
@@ -51,7 +52,8 @@
 
   // It's ridiculously faster to write to a string and then write that to
   // disk in one operation than to use an fstream here.
-  std::stringstream rules;
+  StringOutputBuffer storage;
+  std::ostream rules(&storage);
 
   // Call out to the correct sub-type of writer. Binary targets need to be
   // written to separate files for compiler flag scoping, but other target
@@ -101,8 +103,7 @@
     SourceFile ninja_file = GetNinjaFileForTarget(target);
     base::FilePath full_ninja_file =
         settings->build_settings()->GetFullPath(ninja_file);
-    base::CreateDirectory(full_ninja_file.DirName());
-    WriteFileIfChanged(full_ninja_file, rules.str(), nullptr);
+    storage.WriteToFileIfChanged(full_ninja_file, nullptr);
 
     EscapeOptions options;
     options.mode = ESCAPE_NINJA;
@@ -117,7 +118,7 @@
   }
 
   // No separate file required, just return the rules.
-  return rules.str();
+  return storage.str();
 }
 
 void NinjaTargetWriter::WriteEscapedSubstitution(const Substitution* type) {
diff --git a/src/gn/qt_creator_writer.cc b/src/gn/qt_creator_writer.cc
index f5c997a..b0fa05c 100644
--- a/src/gn/qt_creator_writer.cc
+++ b/src/gn/qt_creator_writer.cc
@@ -19,6 +19,7 @@
 #include "gn/filesystem_utils.h"
 #include "gn/label.h"
 #include "gn/loader.h"
+#include "gn/string_output_buffer.h"
 
 namespace {
 base::FilePath::CharType kProjectDirName[] =
@@ -270,10 +271,11 @@
 void QtCreatorWriter::GenerateFile(const base::FilePath::CharType* suffix,
                                    const std::set<std::string>& items) {
   const base::FilePath file_path = project_prefix_.AddExtension(suffix);
-  std::ostringstream output;
+  StringOutputBuffer storage;
+  std::ostream output(&storage);
   for (const std::string& item : items)
     output << item << std::endl;
-  WriteFileIfChanged(file_path, output.str(), &err_);
+  storage.WriteToFileIfChanged(file_path, &err_);
 }
 
 void QtCreatorWriter::Run() {
diff --git a/src/gn/runtime_deps.cc b/src/gn/runtime_deps.cc
index 3b6d683..25eb2ef 100644
--- a/src/gn/runtime_deps.cc
+++ b/src/gn/runtime_deps.cc
@@ -19,6 +19,7 @@
 #include "gn/output_file.h"
 #include "gn/scheduler.h"
 #include "gn/settings.h"
+#include "gn/string_output_buffer.h"
 #include "gn/switches.h"
 #include "gn/target.h"
 #include "gn/trace.h"
@@ -202,12 +203,13 @@
   base::FilePath data_deps_file =
       target->settings()->build_settings()->GetFullPath(output_as_source);
 
-  std::stringstream contents;
+  StringOutputBuffer storage;
+  std::ostream contents(&storage);
   for (const auto& pair : ComputeRuntimeDeps(target))
     contents << pair.first.value() << std::endl;
 
   ScopedTrace trace(TraceItem::TRACE_FILE_WRITE, output_as_source.value());
-  return WriteFileIfChanged(data_deps_file, contents.str(), err);
+  return storage.WriteToFileIfChanged(data_deps_file, err);
 }
 
 }  // namespace
diff --git a/src/gn/rust_project_writer.cc b/src/gn/rust_project_writer.cc
index ee62479..c11f967 100644
--- a/src/gn/rust_project_writer.cc
+++ b/src/gn/rust_project_writer.cc
@@ -12,7 +12,6 @@
 #include "base/json/string_escape.h"
 #include "gn/builder.h"
 #include "gn/deps_iterator.h"
-#include "gn/filesystem_utils.h"
 #include "gn/ninja_target_command_util.h"
 #include "gn/rust_project_writer_helpers.h"
 #include "gn/rust_tool.h"
@@ -70,12 +69,7 @@
   std::ostream out(&out_buffer);
 
   RenderJSON(build_settings, all_targets, out);
-
-  if (out_buffer.ContentsEqual(output_path)) {
-    return true;
-  }
-
-  return out_buffer.WriteToFile(output_path, err);
+  return out_buffer.WriteToFileIfChanged(output_path, err);
 }
 
 // Map of Targets to their index in the crates list (for linking dependencies to
diff --git a/src/gn/string_output_buffer.cc b/src/gn/string_output_buffer.cc
index 09913ce..c5d91ff 100644
--- a/src/gn/string_output_buffer.cc
+++ b/src/gn/string_output_buffer.cc
@@ -115,3 +115,11 @@
   }
   return success;
 }
+
+bool StringOutputBuffer::WriteToFileIfChanged(const base::FilePath& file_path,
+                                              Err* err) const {
+  if (ContentsEqual(file_path))
+    return true;
+
+  return WriteToFile(file_path, err);
+}
diff --git a/src/gn/string_output_buffer.h b/src/gn/string_output_buffer.h
index 5e89250..2338860 100644
--- a/src/gn/string_output_buffer.h
+++ b/src/gn/string_output_buffer.h
@@ -66,6 +66,10 @@
   // Write the contents of this instance to a file at |file_path|.
   bool WriteToFile(const base::FilePath& file_path, Err* err) const;
 
+  // Write the contents of this instance to a file at |file_path| unless the
+  // file already exists and the contents are equal.
+  bool WriteToFileIfChanged(const base::FilePath& file_path, Err* err) const;
+
   static size_t GetPageSizeForTesting() { return kPageSize; }
 
  protected:
diff --git a/src/gn/visual_studio_writer.cc b/src/gn/visual_studio_writer.cc
index 6ee56e8..f6ea9d2 100644
--- a/src/gn/visual_studio_writer.cc
+++ b/src/gn/visual_studio_writer.cc
@@ -25,6 +25,7 @@
 #include "gn/parse_tree.h"
 #include "gn/path_output.h"
 #include "gn/standard_out.h"
+#include "gn/string_output_buffer.h"
 #include "gn/target.h"
 #include "gn/variables.h"
 #include "gn/visual_studio_utils.h"
@@ -411,7 +412,8 @@
       FilePathToUTF8(build_settings_->GetFullPath(target->label().dir())),
       project_config_platform));
 
-  std::stringstream vcxproj_string_out;
+  StringOutputBuffer vcxproj_storage;
+  std::ostream vcxproj_string_out(&vcxproj_storage);
   SourceFileCompileTypePairs source_types;
   if (!WriteProjectFileContents(vcxproj_string_out, *projects_.back(), target,
                                 ninja_extra_args, &source_types, err)) {
@@ -422,13 +424,15 @@
   // Only write the content to the file if it's different. That is
   // both a performance optimization and more importantly, prevents
   // Visual Studio from reloading the projects.
-  if (!WriteFileIfChanged(vcxproj_path, vcxproj_string_out.str(), err))
+  if (!vcxproj_storage.WriteToFileIfChanged(vcxproj_path, err))
     return false;
 
   base::FilePath filters_path = UTF8ToFilePath(vcxproj_path_str + ".filters");
-  std::stringstream filters_string_out;
+
+  StringOutputBuffer filters_storage;
+  std::ostream filters_string_out(&filters_storage);
   WriteFiltersFileContents(filters_string_out, target, source_types);
-  return WriteFileIfChanged(filters_path, filters_string_out.str(), err);
+  return filters_storage.WriteToFileIfChanged(filters_path, err);
 }
 
 bool VisualStudioWriter::WriteProjectFileContents(
@@ -732,13 +736,14 @@
 
   base::FilePath sln_path = build_settings_->GetFullPath(sln_file);
 
-  std::stringstream string_out;
+  StringOutputBuffer storage;
+  std::ostream string_out(&storage);
   WriteSolutionFileContents(string_out, sln_path.DirName());
 
   // Only write the content to the file if it's different. That is
   // both a performance optimization and more importantly, prevents
   // Visual Studio from reloading the projects.
-  return WriteFileIfChanged(sln_path, string_out.str(), err);
+  return storage.WriteToFileIfChanged(sln_path, err);
 }
 
 void VisualStudioWriter::WriteSolutionFileContents(
diff --git a/src/gn/xcode_writer.cc b/src/gn/xcode_writer.cc
index a5650fa..27f28e1 100644
--- a/src/gn/xcode_writer.cc
+++ b/src/gn/xcode_writer.cc
@@ -31,6 +31,7 @@
 #include "gn/scheduler.h"
 #include "gn/settings.h"
 #include "gn/source_file.h"
+#include "gn/string_output_buffer.h"
 #include "gn/substitution_writer.h"
 #include "gn/target.h"
 #include "gn/value.h"
@@ -489,7 +490,8 @@
   if (source_file.is_null())
     return false;
 
-  std::stringstream out;
+  StringOutputBuffer storage;
+  std::ostream out(&storage);
   out << "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n"
       << "<Workspace\n"
       << "   version = \"1.0\">\n"
@@ -498,8 +500,8 @@
       << "   </FileRef>\n"
       << "</Workspace>\n";
 
-  return WriteFileIfChanged(build_settings_->GetFullPath(source_file),
-                            out.str(), err);
+  return storage.WriteToFileIfChanged(build_settings_->GetFullPath(source_file),
+                                      err);
 }
 
 bool XcodeWorkspace::WriteSettingsFile(const std::string& name,
@@ -511,7 +513,8 @@
   if (source_file.is_null())
     return false;
 
-  std::stringstream out;
+  StringOutputBuffer storage;
+  std::ostream out(&storage);
   out << "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n"
       << "<!DOCTYPE plist PUBLIC \"-//Apple//DTD PLIST 1.0//EN\" "
       << "\"http://www.apple.com/DTDs/PropertyList-1.0.dtd\">\n"
@@ -530,8 +533,8 @@
   out << "</dict>\n"
       << "</plist>\n";
 
-  return WriteFileIfChanged(build_settings_->GetFullPath(source_file),
-                            out.str(), err);
+  return storage.WriteToFileIfChanged(build_settings_->GetFullPath(source_file),
+                                      err);
 }
 
 // Class responsible for constructing and writing the .xcodeproj from the
@@ -844,11 +847,12 @@
   if (pbxproj_file.is_null())
     return false;
 
-  std::stringstream pbxproj_string_out;
+  StringOutputBuffer storage;
+  std::ostream pbxproj_string_out(&storage);
   WriteFileContent(pbxproj_string_out);
 
-  if (!WriteFileIfChanged(build_settings_->GetFullPath(pbxproj_file),
-                          pbxproj_string_out.str(), err)) {
+  if (!storage.WriteToFileIfChanged(build_settings_->GetFullPath(pbxproj_file),
+                                    err)) {
     return false;
   }