scheduler: Only prioritize rAF if it is fast

scheduler: Only prioritize rAF if it is fast

To avoid starving other tasks, only prioritize main thread compositing (i.e.,
requestAnimationFrame) if there is more than 80% idle time left in a frame. This can
reduce animation frame rate on sites which can't keep up with the display refresh
rate, but will ensure other tasks (e.g., postMessage) aren't starved as a
side-effect.

BUG=600385
Review-Url: https://codereview.chromium.org/1914373004
Cr-Commit-Position: refs/heads/master@{#391221}
(cherry picked from commit 6f3d26fe1385dc74f22bf2cf6bddc6830dd00d6c)

Committed: https://chromium.googlesource.com/chromium/src/+/bf63388e22acf3290e8c3eb8891dd8bfbcc3f86b

[Sami, 2016-05-05 12:53:33]

Description was changed from

==========
scheduler: Only prioritize rAF if it is fast

To avoid starving other tasks, only prioritize main thread compositing (i.e.,
requestAnimationFrame) if there is more than 80% idle time left in a frame. This
can
reduce animation frame rate on sites which can't keep up with the display
refresh
rate, but will ensure other tasks (e.g., postMessage) aren't starved as a
side-effect.

BUG=600385

Review-Url: https://codereview.chromium.org/1914373004
Cr-Commit-Position: refs/heads/master@{#391221}
(cherry picked from commit 6f3d26fe1385dc74f22bf2cf6bddc6830dd00d6c)
==========

to

==========
scheduler: Only prioritize rAF if it is fast

To avoid starving other tasks, only prioritize main thread compositing (i.e.,
requestAnimationFrame) if there is more than 80% idle time left in a frame. This
can
reduce animation frame rate on sites which can't keep up with the display
refresh
rate, but will ensure other tasks (e.g., postMessage) aren't starved as a
side-effect.

BUG=600385

Review-Url: https://codereview.chromium.org/1914373004
Cr-Commit-Position: refs/heads/master@{#391221}
(cherry picked from commit 6f3d26fe1385dc74f22bf2cf6bddc6830dd00d6c)

Committed:
https://chromium.googlesource.com/chromium/src/+/bf63388e22acf3290e8c3eb8891d...
==========

[Sami, 2016-05-05 12:53:35]

Committed patchset #1 (id:1) manually as
bf63388e22acf3290e8c3eb8891dd8bfbcc3f86b.