cc: Emulate BeginFrame in OutputSurfaces that don't support it natively

cc/scheduler/scheduler_state_machine.cc

Index: cc/scheduler/scheduler_state_machine.cc
diff --git a/cc/scheduler/scheduler_state_machine.cc b/cc/scheduler/scheduler_state_machine.cc
index 01252dd7aff1c21a0330eb5c9598a567658a6eb1..2ff70bbdcbcaddf6b905d05a9946bafdf451db71 100644
--- a/cc/scheduler/scheduler_state_machine.cc
+++ b/cc/scheduler/scheduler_state_machine.cc
@@ -332,6 +332,11 @@ void SchedulerStateMachine::SetMainThreadNeedsLayerTextures() {
 }
 
 bool SchedulerStateMachine::BeginFrameNeededByImplThread() const {
+  // We should proactively request a BeginFrame if a commit is pending.
+  if (needs_commit_ || needs_forced_commit_ ||
+      commit_state_ != COMMIT_STATE_IDLE)
+    return true;
+
   // If we have a pending tree, need to keep getting notifications until
   // the tree is ready to be swapped.
   if (has_pending_tree_)