Revert of Remove swap ack throttling to regain performance regression on freon

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 9d425d498e46aba5c2f9ddef7fe56921fb0133aa..41de95dc2b61e06566046cb38aeb52fbe92d1d7b 100644
--- a/cc/scheduler/scheduler_state_machine.cc
+++ b/cc/scheduler/scheduler_state_machine.cc
@@ -437,6 +437,14 @@
   if (!HasInitializedOutputSurface())
     return false;
 
+  // SwapAck throttle the BeginMainFrames unless we just swapped.
+  // TODO(brianderson): Remove this restriction to improve throughput.
+  bool just_swapped_in_deadline =
+      begin_impl_frame_state_ == BEGIN_IMPL_FRAME_STATE_INSIDE_DEADLINE &&
+      did_perform_swap_in_last_draw_;
+  if (pending_swaps_ >= max_pending_swaps_ && !just_swapped_in_deadline)
+    return false;
+
   if (skip_begin_main_frame_to_reduce_latency_)
     return false;