Fix RenderWidgetHostViewAura as observer of CompositorVSyncManager

Fix RenderWidgetHostViewAura as observer of CompositorVSyncManager

RWHVA needs to deregister itself properly as an observer of
CompositorVSyncManager even if the compositor itself is destroyed.  Do this
properly by keeping a reference to the CompositorVSyncManager.

BUG=343199
TEST=local build, run on desktop Linux, Win7

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=251017

[sheu, 2014-02-13 01:31:59]

piman@: to fix the Windows crash.  PTAL, thanks!

[piman, 2014-02-13 01:44:36]

https://chromiumcodereview.appspot.com/152983004/diff/60001/content/browser/r...
File content/browser/renderer_host/render_widget_host_view_aura.cc (right):

https://chromiumcodereview.appspot.com/152983004/diff/60001/content/browser/r...
content/browser/renderer_host/render_widget_host_view_aura.cc:3538: if
(compositor) {
You need to deregister yourself from vsync_manager_ here (or in
RemovingFromRootWindow) for the case where we move between RootWindows.

[sheu, 2014-02-13 01:52:35]

Done.  PTAL

[piman, 2014-02-13 02:06:44]

lgtm

https://chromiumcodereview.appspot.com/152983004/diff/130001/content/browser/...
File content/browser/renderer_host/render_widget_host_view_aura.cc (right):

https://chromiumcodereview.appspot.com/152983004/diff/130001/content/browser/...
content/browser/renderer_host/render_widget_host_view_aura.cc:3535: if
(compositor) {
nit: maybe DCHECK(!vsync_manager_.get()) here, and in the destructor?

[sheu, 2014-02-13 02:10:49]

The CQ bit was checked by sheu@chromium.org

[commit-bot: I haz the power, 2014-02-13 02:18:21]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/sheu@chromium.org/152983004/220001

[commit-bot: I haz the power, 2014-02-13 15:18:39]

Change committed as 251017