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

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 e73508ce1ab1fb198c9b69ff0e65609a3e637e8e..5011ef862dd0d50b14046dc414b4aaba2fdbd0fa 100644
--- a/cc/scheduler/scheduler_state_machine.cc
+++ b/cc/scheduler/scheduler_state_machine.cc
@@ -42,9 +42,10 @@ SchedulerStateMachine::SchedulerStateMachine(const SchedulerSettings& settings)
       last_frame_number_begin_main_frame_sent_(-1),
       last_frame_number_invalidate_compositor_frame_sink_performed_(-1),
       draw_funnel_(false),
-      send_begin_main_frame_funnel_(true),
+      did_send_begin_main_frame_for_current_frame_(true),
       invalidate_compositor_frame_sink_funnel_(false),
       impl_side_invalidation_funnel_(false),
+      did_do_idle_work_(false),
       prepare_tiles_funnel_(0),
       consecutive_checkerboard_animations_(0),
       pending_submit_frames_(0),
@@ -194,6 +195,8 @@ const char* SchedulerStateMachine::ActionToString(Action action) {
       return "ACTION_INVALIDATE_COMPOSITOR_FRAME_SINK";
     case ACTION_PERFORM_IMPL_SIDE_INVALIDATION:
       return "ACTION_PERFORM_IMPL_SIDE_INVALIDATION";
+    case ACTION_DO_SHORT_IDLE_WORK:
+      return "ACTION_DO_SHORT_IDLE_WORK";
   }
   NOTREACHED();
   return "???";
@@ -244,8 +247,9 @@ void SchedulerStateMachine::AsValueInto(
       "last_begin_frame_sequence_number_compositor_frame_was_fresh",
       last_begin_frame_sequence_number_compositor_frame_was_fresh_);
   state->SetBoolean("funnel: draw_funnel", draw_funnel_);
-  state->SetBoolean("funnel: send_begin_main_frame_funnel",
-                    send_begin_main_frame_funnel_);
+  state->SetBoolean("funnel: did_send_begin_main_frame",
+                    did_send_begin_main_frame_for_current_frame_);
+  state->SetBoolean("funnel: did_do_idle_work", did_do_idle_work_);
   state->SetInteger("funnel: prepare_tiles_funnel", prepare_tiles_funnel_);
   state->SetBoolean("funnel: invalidate_compositor_frame_sink_funnel",
                     invalidate_compositor_frame_sink_funnel_);
@@ -428,6 +432,33 @@ bool SchedulerStateMachine::ShouldActivatePendingTree() const {
   return pending_tree_is_ready_for_activation_;
 }
 
+bool SchedulerStateMachine::ShouldDoShortIdleWork() const {
+  // BeginMainFrame already triggers idle work, so we don't need to schedule
+  // extra idle work here.
+  if (needs_begin_main_frame_ || did_send_begin_main_frame_for_current_frame_)
+    return false;
+
+  // Only schedule extra idle work when we're visible.
+  if (!visible_)
+    return false;
+
+  // There are no BeginImplFrames while BeginFrameSource is paused,
+  // so should also stop scheduling extra idle work.
+  if (begin_frame_source_paused_)
+    return false;
+
+  // Do not do idle work too many times in a single frame or before
+  // the first BeginFrame.
+  if (did_do_idle_work_)
+    return false;
+
+  // If a BeginMainFrame is in progress, don't do any extra idle work.
+  if (begin_main_frame_state_ != BEGIN_MAIN_FRAME_STATE_IDLE)
+    return false;
+
+  return true;
+}
+
 bool SchedulerStateMachine::CouldSendBeginMainFrame() const {
   if (!needs_begin_main_frame_)
     return false;
@@ -454,7 +485,7 @@ bool SchedulerStateMachine::ShouldSendBeginMainFrame() const {
 
   // Do not send begin main frame too many times in a single frame or before
   // the first BeginFrame.
-  if (send_begin_main_frame_funnel_)
+  if (did_send_begin_main_frame_for_current_frame_)
     return false;
 
   // Only send BeginMainFrame when there isn't another commit pending already.
@@ -598,6 +629,8 @@ SchedulerStateMachine::Action SchedulerStateMachine::NextAction() const {
     return ACTION_INVALIDATE_COMPOSITOR_FRAME_SINK;
   if (ShouldBeginCompositorFrameSinkCreation())
     return ACTION_BEGIN_COMPOSITOR_FRAME_SINK_CREATION;
+  if (ShouldDoShortIdleWork())
+    return ACTION_DO_SHORT_IDLE_WORK;
   return ACTION_NONE;
 }
 
@@ -683,15 +716,22 @@ void SchedulerStateMachine::WillSendBeginMainFrame() {
   DCHECK(!has_pending_tree_ || settings_.main_frame_before_activation_enabled);
   DCHECK(visible_);
   DCHECK(!begin_frame_source_paused_);
-  DCHECK(!send_begin_main_frame_funnel_);
+  DCHECK(!did_send_begin_main_frame_for_current_frame_);
   begin_main_frame_state_ = BEGIN_MAIN_FRAME_STATE_SENT;
   needs_begin_main_frame_ = false;
-  send_begin_main_frame_funnel_ = true;
+  did_send_begin_main_frame_for_current_frame_ = true;
   last_frame_number_begin_main_frame_sent_ = current_frame_number_;
   last_begin_frame_sequence_number_begin_main_frame_sent_ =
       begin_frame_sequence_number_;
 }
 
+void SchedulerStateMachine::WillDoShortIdleWork() {
+  DCHECK(visible_);
+  DCHECK(!begin_frame_source_paused_);
+  DCHECK(!did_do_idle_work_);
+  did_do_idle_work_ = true;
+}
+
 void SchedulerStateMachine::WillCommit(bool commit_has_no_updates) {
   bool can_have_pending_tree =
       commit_has_no_updates &&
@@ -1047,7 +1087,8 @@ void SchedulerStateMachine::OnBeginImplFrame(uint32_t source_id,
   needs_one_begin_impl_frame_ = false;
 
   // Clear funnels for any actions we perform during the frame.
-  send_begin_main_frame_funnel_ = false;
+  did_do_idle_work_ = false;
+  did_send_begin_main_frame_for_current_frame_ = false;
   invalidate_compositor_frame_sink_funnel_ = false;
   impl_side_invalidation_funnel_ = false;
 
@@ -1085,7 +1126,7 @@ void SchedulerStateMachine::OnBeginImplFrameIdle() {
   // If we're entering a state where we won't get BeginFrames set all the
   // funnels so that we don't perform any actions that we shouldn't.
   if (!BeginFrameNeeded())
-    send_begin_main_frame_funnel_ = true;
+    did_send_begin_main_frame_for_current_frame_ = true;
 
   // Synchronous compositor finishes BeginFrames before triggering their
   // deadline. Therefore, we update sequence numbers when becoming idle, before