Add begin frame paused signal

This avoids a deadlock situation in android webview where
begin frames have stopped, but the blink main thread is blocked
indefinitely waiting for activation. See bug for details.

Plumb a signal that the BeginFrameSource is paused directly
through BeginFrameSourceObserver, and force activate any
pending activations when paused. This is similar to when
compositor becomes invisible, but BFS allows webview send
the signal without a hop to blink main thread.

BUG=539373
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1536353003

Cr-Commit-Position: refs/heads/master@{#369238}

2 files changed, 7 insertions, 0 deletions

diff --git a/cc/surfaces/display_scheduler.cc b/cc/surfaces/display_scheduler.cc
index feb84ea..f87d4fb 100644
--- a/cc/surfaces/display_scheduler.cc
+++ b/cc/surfaces/display_scheduler.cc
@@ -152,6 +152,12 @@ bool DisplayScheduler::OnBeginFrameDerivedImpl(const BeginFrameArgs& args) {
   return true;
 }
 
+void DisplayScheduler::OnBeginFrameSourcePausedChanged(bool paused) {
+  // BeginFrameSources used with DisplayScheduler do not make use of this
+  // feature.
+  NOTIMPLEMENTED();
+}
+
 base::TimeTicks DisplayScheduler::DesiredBeginFrameDeadlineTime() {
   if (output_surface_lost_) {
     TRACE_EVENT_INSTANT0("cc", "Lost output surface", TRACE_EVENT_SCOPE_THREAD);
diff --git a/cc/surfaces/display_scheduler.h b/cc/surfaces/display_scheduler.h
index 838af40..cb8a365 100644
--- a/cc/surfaces/display_scheduler.h
+++ b/cc/surfaces/display_scheduler.h
@@ -48,6 +48,7 @@ class CC_SURFACES_EXPORT DisplayScheduler : public BeginFrameObserverBase {
 
   // BeginFrameObserverBase implementation
   bool OnBeginFrameDerivedImpl(const BeginFrameArgs& args) override;
+  void OnBeginFrameSourcePausedChanged(bool paused) override;
 
   BeginFrameSource* begin_frame_source_for_children() {
     return begin_frame_source_for_children_.get();