Add raster cache metrics to timeline summaries

[flar]

Recently some internal benchmarks have pointed out higher memory usage while using the DisplayList mechanism. In diagnosing the issue locally we realized we are using a lot more cache memory for internal benchmarks like the flutter_gallery. This PR will add statistics for layer and raster cache usage to the standard benchmark measurements we take for flutter_gallery which should alert us to issues in the future.

[flutter-dashboard]

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If you are not sure if you need tests, consider this rule of thumb: the purpose of a test is to make sure someone doesn't accidentally revert the fix. Ask yourself, is there anything in your PR that you feel it is important we not accidentally revert back to how it was before your fix?

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[flar]

The comment about the lack of testing is now obsolete as there are existing tests that I had to modify to get this to pass, so the additions are now tested for.

[flar]

The FrameTiming mods have rolled in from the engine repo and the latest commit now publishes those metrics as well for e2e benchmarks.