Remove synchronous compositeAndReadback() from WebLayerTreeView impls.

Remove synchronous compositeAndReadback() from WebLayerTreeView impls.

Removes it from the RenderWidgetCompositor and
WebLayerTreeViewImplForTesting classes.

Depends on: https://codereview.chromium.org/276753002/

R=piman
BUG=251936
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=269842

[piman, 2014-05-08 22:12:28]

lgtm

[danakj, 2014-05-12 14:28:46]

The CQ bit was checked by danakj@chromium.org

[commit-bot: I haz the power, 2014-05-12 14:29:04]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/danakj@chromium.org/277703002/1

[commit-bot: I haz the power, 2014-05-12 16:23:53]

FYI, CQ is re-trying this CL (attempt #1).
Please consider checking whether the failures are real,
and report flakes to chrome-troopers@google.com.
The failing builders are:
  android_dbg_triggered_tests on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/android_dbg_triggered...)
  ios_dbg_simulator on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/ios_dbg_simulator/bui...)

[commit-bot: I haz the power, 2014-05-12 17:44:44]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-05-12 17:44:44]

Try jobs failed on following builders:
  android_dbg_triggered_tests on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/android_dbg_triggered...)

[danakj, 2014-05-12 18:10:41]

Oh good this test is also failing on https://codereview.chromium.org/274453002/,
it's not magically somehow related to this change.

[danakj, 2014-05-12 18:10:51]

The CQ bit was checked by danakj@chromium.org

[commit-bot: I haz the power, 2014-05-12 18:11:15]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/danakj@chromium.org/277703002/1

[commit-bot: I haz the power, 2014-05-12 19:25:55]

Change committed as 269842