Create a new action triggered when a BeginMainFrame is not expected before vsync

cc/scheduler/scheduler.cc

Index: cc/scheduler/scheduler.cc
diff --git a/cc/scheduler/scheduler.cc b/cc/scheduler/scheduler.cc
index 93525696d74a3c0e0b7b79e14824ac9bb150e6a7..5466ca493b60c6d37f2a5346c0324773a3d90468 100644
--- a/cc/scheduler/scheduler.cc
+++ b/cc/scheduler/scheduler.cc
@@ -629,6 +629,10 @@ void Scheduler::ProcessScheduledActions() {
         // TODO(brianderson): Pass begin_main_frame_args_ directly to client.
         client_->ScheduledActionSendBeginMainFrame(begin_main_frame_args_);
         break;
+      case SchedulerStateMachine::ACTION_DO_IDLE_WORK:
+        state_machine_.WillDoIdleWork();
+        BeginImplFrameNotExpectedSoon();

[Sami, 2017/03/20 16:58:49]

Let's introduce a new notification which kicks off a short idle period rather
than a long one to avoid accidental jank.

+        break;
       case SchedulerStateMachine::ACTION_COMMIT: {
         bool commit_has_no_updates = false;
         state_machine_.WillCommit(commit_has_no_updates);