cc: Simplify SetNeedsBeginFrames code in scheduler.

cc/scheduler/scheduler.cc

Index: cc/scheduler/scheduler.cc
diff --git a/cc/scheduler/scheduler.cc b/cc/scheduler/scheduler.cc
index 25c3d04f1a661ce27b3e1e66a83e7ce9b7b94077..3337b38227b0c8b5406a31f612ce3f2b005c94bc 100644
--- a/cc/scheduler/scheduler.cc
+++ b/cc/scheduler/scheduler.cc
@@ -299,19 +299,21 @@ base::TimeTicks Scheduler::LastBeginImplFrameTime() {
   return begin_impl_frame_args_.frame_time;
 }
 
-void Scheduler::SetupNextBeginFrameIfNeeded() {
-  if (!task_runner_.get())
+void Scheduler::SetNeedsBeginFrameIfNeeded() {
+  // Never call SetNeedsBeginFrames if the frame source already has the right
+  // value.
+  if (frame_source_->NeedsBeginFrames() == state_machine_.BeginFrameNeeded())
     return;
 
-  if (state_machine_.ShouldSetNeedsBeginFrames(
-          frame_source_->NeedsBeginFrames())) {
-    frame_source_->SetNeedsBeginFrames(state_machine_.BeginFrameNeeded());
-    if (!frame_source_->NeedsBeginFrames()) {
-      client_->SendBeginMainFrameNotExpectedSoon();
-    }
+  // Always call SetNeedsBeginFrames(true). Only call SetNeedsBeginFrames(false)
+  // in between BeginFrames i.e. when begin_impl_frame_state is IDLE.
+  if (state_machine_.BeginFrameNeeded()) {
+    frame_source_->SetNeedsBeginFrames(true);
+  } else if (state_machine_.begin_impl_frame_state() ==
+             SchedulerStateMachine::BEGIN_IMPL_FRAME_STATE_IDLE) {
+    frame_source_->SetNeedsBeginFrames(false);
+    client_->SendBeginMainFrameNotExpectedSoon();
   }
-
-  SetupPollingMechanisms();
 }
 
 // We may need to poll when we can't rely on BeginFrame to advance certain
@@ -686,14 +688,19 @@ void Scheduler::ProcessScheduledActions() {
   tracked_objects::ScopedTracker tracking_profile10(
       FROM_HERE_WITH_EXPLICIT_FUNCTION(
           "461509 Scheduler::ProcessScheduledActions10"));
-  SetupNextBeginFrameIfNeeded();
+
+  SetupPollingMechanisms();
+
   client_->DidAnticipatedDrawTimeChange(AnticipatedDrawTime());
 
   // TODO(robliao): Remove ScopedTracker below once crbug.com/461509 is fixed.
   tracked_objects::ScopedTracker tracking_profile11(
       FROM_HERE_WITH_EXPLICIT_FUNCTION(
           "461509 Scheduler::ProcessScheduledActions11"));
+
   RescheduleBeginImplFrameDeadlineIfNeeded();
+
+  SetNeedsBeginFrameIfNeeded();
 }
 
 scoped_refptr<base::trace_event::ConvertableToTraceFormat> Scheduler::AsValue()