To work on Skia inside a Chromium checkout, run the following:
cd chromium/src/third_party/skia python2 tools/git-sync-deps bin/gn gen out/Debug
The second command does a minimal “just sync the DEPS” emulation of gclient sync for Skia into chromium/src/third_party/skia/third_party. After that, ninja -C out/Debug dm in chromium/src/third_party/skia will get you rolling.
We no longer recommend the .gclient file manipulation to have Chromium DEPS also sync Skia‘s DEPS. Most of those DEPS are for building and testing only; Chromium doesn’t need any of them, and it can be confusing and problematic if they somehow get mixed into the Chromium build.