We report largely redundant data in CompositorFrameMetadata. Activation dependencies are listed twice: One in |activation_dependencies| and once in referenced_surfaces. Part of the problem is not all referenced_surfaces are activation_dependencies: a CompositorFrame can retain child surfaces that are not in the viewport (say minimized Chrome OS windows).

I had previously attempted to get rid of activation_dependencies and failed as a result:

https://chromium-review.googlesource.com/c/chromium/src/+/1145496

One possible solution is to introduce an additional |activation_requirement| for each referenced surface.