Weight subframe jank score in proportion to its geometry.

This applies the appropriate weight to the scores reported to the RenderFrame,
but these scores are not yet summed in the browser for UKM/UMA.

The scores reported by the web perf API are not affected.

Bug: 581518
Change-Id: I5182d840f980278c00aad39c4957a853a417b7a0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1526422
Commit-Queue: Steve Kobes <skobes@chromium.org>
Reviewed-by: Timothy Dresser <tdresser@chromium.org>
Cr-Commit-Position: refs/heads/master@{#642190}
3 files changed