cc: Allow the main thread to cancel commits

Add a new SetNeedsUpdateLayers that triggers the commit flow, but is
abortable if update layers doesn't actually make any changes.  This
allows the main thread to abort a begin frame.  This happens in the case
of scroll updates from the compositor thread or invalidations.

There was previously an abort begin frame call for when a visibility
message and a begin frame message were posted simultaneously, but it
incorrectly applied the scrolls and scales without informing the
compositor thread that these had already been consumed.  To fix this,
the abort message passes back a boolean about whether or not the
commit was aborted (and needed to be sent again) or was handled
(and the scrolls and scales processed).

To avoid a deluge of begin frames (in the commit sense) from the
scheduler, the scheduler has been adjusted to wait until the next begin
frame (in the vsync signal sense) so that these calls can be throttled.
Otherwise, the scheduler will just keep trying to begin frame.

R=brianderson@chromium.org, danakj@chromium.org
BUG=256381

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=213338

Review URL: https://chromiumcodereview.appspot.com/19106007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@214314 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 1 insertions, 0 deletions

diff --git a/cc/trees/layer_tree_host_unittest_damage.cc b/cc/trees/layer_tree_host_unittest_damage.cc
index 523eecd..e8ae7a2 100644
--- a/cc/trees/layer_tree_host_unittest_damage.cc
+++ b/cc/trees/layer_tree_host_unittest_damage.cc
@@ -87,6 +87,7 @@ class LayerTreeHostDamageTestNoDamageDoesNotSwap
       case 3:
         // Cause non-visible damage.
         content_->SetNeedsDisplayRect(gfx::Rect(1990, 1990, 10, 10));
+        layer_tree_host()->SetNeedsCommit();
         break;
     }
   }