These files define the inspector protocol, not necessarily what is implemented in Cobalt.
https://chromedevtools.github.io/devtools-protocol/

These files were originally taken from Blink in the Chromium repo as of
August 16, 2018 to roughly correspond to Chrome stable 68.0.3440.118.
https://chromium.googlesource.com/chromium/src.git/+/88c90a9cfb8c958d62ef5c580ce057f6f541ec3a/third_party/blink/renderer/core

inspector/BUILD.gn (rules ported to GYP)
inspector/browser_protocol-1.3.json
inspector/browser_protocol.pdl
html/aria_properties.json5
css/CSSProperties.json5