cc: Throttle swaps in Scheduler instead of OutputSurface

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 0ff27f4a1355979515c780722943536178ed73eb..0863849de2b545bf098b89e35e5349463564318d 100644
--- a/cc/scheduler/scheduler_state_machine.cc
+++ b/cc/scheduler/scheduler_state_machine.cc
@@ -28,6 +28,8 @@ SchedulerStateMachine::SchedulerStateMachine(const SchedulerSettings& settings)
       last_frame_number_update_visible_tiles_was_called_(-1),
       manage_tiles_funnel_(0),
       consecutive_checkerboard_animations_(0),
+      max_pending_swaps_(1),
+      pending_swaps_(0),
       needs_redraw_(false),
       needs_manage_tiles_(false),
       swap_used_incomplete_tile_(false),
@@ -245,6 +247,8 @@ scoped_ptr<base::Value> SchedulerStateMachine::AsValue() const  {
   minor_state->SetInteger("manage_tiles_funnel", manage_tiles_funnel_);
   minor_state->SetInteger("consecutive_checkerboard_animations",
                           consecutive_checkerboard_animations_);
+  minor_state->SetInteger("max_pending_swaps_", max_pending_swaps_);
+  minor_state->SetInteger("pending_swaps_", pending_swaps_);
   minor_state->SetBoolean("needs_redraw", needs_redraw_);
   minor_state->SetBoolean("needs_manage_tiles", needs_manage_tiles_);
   minor_state->SetBoolean("swap_used_incomplete_tile",
@@ -390,6 +394,10 @@ bool SchedulerStateMachine::ShouldDraw() const {
   if (HasSwappedThisFrame())
     return false;
 
+  // Do not queue too many swaps.
+  if (pending_swaps_ >= max_pending_swaps_)
+    return false;
+
   // Except for the cases above, do not draw outside of the BeginImplFrame
   // deadline.
   if (begin_impl_frame_state_ != BEGIN_IMPL_FRAME_STATE_INSIDE_DEADLINE)
@@ -507,6 +515,11 @@ bool SchedulerStateMachine::ShouldSendBeginMainFrame() const {
   if (!HasInitializedOutputSurface())
     return false;
 
+  // SwapAck throttle the BeginMainFrames
+  // TODO(brianderson): Remove this restriction to improve throughput.
+  if (pending_swaps_ >= max_pending_swaps_)
+    return false;
+
   if (skip_begin_main_frame_to_reduce_latency_)
     return false;
 
@@ -855,8 +868,7 @@ bool SchedulerStateMachine::SupportsProactiveBeginFrame() const {
   // Both the synchronous compositor and disabled vsync settings
   // make it undesirable to proactively request BeginImplFrames.
   // If this is true, the scheduler should poll.
-  return !settings_.using_synchronous_renderer_compositor &&
-         settings_.throttle_frame_production;
+  return !settings_.using_synchronous_renderer_compositor;
 }
 
 // These are the cases where we definitely (or almost definitely) have a
@@ -971,6 +983,10 @@ bool SchedulerStateMachine::ShouldTriggerBeginImplFrameDeadlineEarly() const {
   if (output_surface_state_ == OUTPUT_SURFACE_LOST)
     return true;
 
+  // SwapAck throttle the deadline since we wont draw and swap anyway.
+  if (pending_swaps_ >= max_pending_swaps_)
+    return false;
+
   if (active_tree_needs_first_draw_)
     return true;
 
@@ -1059,11 +1075,26 @@ void SchedulerStateMachine::SetNeedsManageTiles() {
   }
 }
 
+void SchedulerStateMachine::SetMaxSwapsPending(int max) {
+  max_pending_swaps_ = max;
+}
+
+void SchedulerStateMachine::DidSwapBuffers() {
+  pending_swaps_++;
+  DCHECK_LE(pending_swaps_, max_pending_swaps_);
+}
+
 void SchedulerStateMachine::SetSwapUsedIncompleteTile(
     bool used_incomplete_tile) {
   swap_used_incomplete_tile_ = used_incomplete_tile;
 }
 
+void SchedulerStateMachine::OnSwapBuffersComplete() {
+  DCHECK(HasInitializedOutputSurface());
+  DCHECK_GT(pending_swaps_, 0);
+  pending_swaps_--;
+}
+
 void SchedulerStateMachine::SetSmoothnessTakesPriority(
     bool smoothness_takes_priority) {
   smoothness_takes_priority_ = smoothness_takes_priority;
@@ -1178,6 +1209,7 @@ void SchedulerStateMachine::DidLoseOutputSurface() {
     return;
   output_surface_state_ = OUTPUT_SURFACE_LOST;
   needs_redraw_ = false;
+  pending_swaps_ = 0;
 }
 
 void SchedulerStateMachine::NotifyReadyToActivate() {