Add a new hook to WebLayerTreeView for requesting frames.

Add a new hook to WebLayerTreeView for requesting frames.

These will be implemented inside the compositor to allow Blink to signal
that it wants either only BeginMainFrame to run the blink side pipeline,
or that it wants the entire compositor pipeline. This will allow an
early out when requestAnimationFrame (or other frame timed callbacks)
are scheduled but nothing is actually dirty in compositor related state.

Eventually blink will stop calling setNeedsAnimate() entirely and call one
of either setNeedsBeginFrame() or setNeedsCompositorUpdate().

R=chrishtr@chromium.org
BUG=490465
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=197091

[esprehn, 2015-06-12 01:01:39]

esprehn@chromium.org changed reviewers:
+ enne@chromium.org

[esprehn, 2015-06-12 01:01:40]

We can bikeshed the names if you want. :)

[enne (OOO), 2015-06-12 23:35:45]

lgtm

[chrishtr, 2015-06-13 16:10:48]

lgtm

[esprehn, 2015-06-13 20:10:26]

The CQ bit was checked by esprehn@chromium.org

[commit-bot: I haz the power, 2015-06-13 20:10:32]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1177363002/1

[commit-bot: I haz the power, 2015-06-13 21:28:21]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=197091