Change input latency result to depend on start of GPU swap

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 8a1af521fbe9657c46740d52f917e73b1caae2dc..f4fcd09a4648a925bdfcf9f7f68706ed89247b8b 100644
--- a/cc/scheduler/scheduler_state_machine.cc
+++ b/cc/scheduler/scheduler_state_machine.cc
@@ -818,6 +818,10 @@ bool SchedulerStateMachine::ProactiveBeginFrameWanted() const {
   return false;
 }
 
+void SchedulerStateMachine::DidSkipBeginImplFrameToReduceLatency() {
+  last_swap_ack_came_after_begin_impl_frame_ = false;
+}
+
 void SchedulerStateMachine::OnBeginImplFrame() {
   begin_impl_frame_state_ = BEGIN_IMPL_FRAME_STATE_BEGIN_FRAME_STARTING;
   current_frame_number_++;
@@ -882,7 +886,6 @@ SchedulerStateMachine::CurrentBeginImplFrameDeadlineMode() const {
 
 bool SchedulerStateMachine::ShouldTriggerBeginImplFrameDeadlineImmediately()
     const {
-  // TODO(brianderson): This should take into account multiple commit sources.
   if (begin_impl_frame_state_ != BEGIN_IMPL_FRAME_STATE_INSIDE_BEGIN_FRAME)
     return false;
 
@@ -994,6 +997,8 @@ void SchedulerStateMachine::DidSwapBuffers() {
 void SchedulerStateMachine::DidSwapBuffersComplete() {
   DCHECK_GT(pending_swaps_, 0);
   pending_swaps_--;
+  last_swap_ack_came_after_begin_impl_frame_ =
+      begin_impl_frame_state_ != BEGIN_IMPL_FRAME_STATE_IDLE;
 }
 
 void SchedulerStateMachine::SetImplLatencyTakesPriority(