chromium/chrome/test/data/webrtc/resources/README

These *sha1 files are resolved by download_from_google_storage. Include this
solution in your .gclient to make downloading happen automatically:

{
  "name"        : "webrtc.DEPS",
  "url"         : "https://chromium.googlesource.com/chromium/deps/webrtc/webrtc.DEPS",
},

The reference video files of the various resolutions must be frame-by-frame
exact copies of each other - otherwise the WebRTC video quality test will
produce incorrect results. The only addition must be the extra frame padding
around the .y4m files.

If you're not a googler, you'll have to comment out the download hook that
downloads from the chrome-webrtc-resources and provide those resources yourself.