Reimplement vsync latency UMA to be based on BeginImplFrame rather than BeginMainFrame

cc/scheduler/scheduler.cc

Index: cc/scheduler/scheduler.cc
diff --git a/cc/scheduler/scheduler.cc b/cc/scheduler/scheduler.cc
index d7d2e8ca6fb2ba6c2adc28c9bd06d25bcb8cc981..0e1b34e39ad9a95c470174dfe2b828953c787b0f 100644
--- a/cc/scheduler/scheduler.cc
+++ b/cc/scheduler/scheduler.cc
@@ -409,20 +409,19 @@ void Scheduler::BeginImplFrameWithDeadline(const BeginFrameArgs& args) {
     return;
   }
 
-  BeginImplFrame(adjusted_args);
+  BeginImplFrame(adjusted_args, now);
 }
 
 void Scheduler::BeginImplFrameSynchronous(const BeginFrameArgs& args) {
   TRACE_EVENT1("cc,benchmark", "Scheduler::BeginImplFrame", "args",
                args.AsValue());
-
   // The main thread currently can't commit before we draw with the
   // synchronous compositor, so never consider the BeginMainFrame fast.
   state_machine_.SetCriticalBeginMainFrameToActivateIsFast(false);
   begin_main_frame_args_ = args;
   begin_main_frame_args_.on_critical_path = !ImplLatencyTakesPriority();
 
-  BeginImplFrame(args);
+  BeginImplFrame(args, Now());
   compositor_timing_history_->WillFinishImplFrame(
       state_machine_.needs_redraw());
   FinishImplFrame();
@@ -463,7 +462,8 @@ void Scheduler::SendBeginFrameAck(const BeginFrameArgs& args,
 // BeginImplFrame starts a compositor frame that will wait up until a deadline
 // for a BeginMainFrame+activation to complete before it times out and draws
 // any asynchronous animation and scroll/pinch updates.
-void Scheduler::BeginImplFrame(const BeginFrameArgs& args) {
+void Scheduler::BeginImplFrame(const BeginFrameArgs& args,
+                               base::TimeTicks now) {
   DCHECK_EQ(state_machine_.begin_impl_frame_state(),
             SchedulerStateMachine::BEGIN_IMPL_FRAME_STATE_IDLE);
   DCHECK(begin_impl_frame_deadline_task_.IsCancelled());
@@ -473,7 +473,7 @@ void Scheduler::BeginImplFrame(const BeginFrameArgs& args) {
   state_machine_.OnBeginImplFrame(args.source_id, args.sequence_number);
   devtools_instrumentation::DidBeginFrame(layer_tree_host_id_);
   compositor_timing_history_->WillBeginImplFrame(
-      state_machine_.NewActiveTreeLikely());
+      state_machine_.NewActiveTreeLikely(), args.frame_time, args.type, now);
   client_->WillBeginImplFrame(begin_impl_frame_tracker_.Current());
 
   ProcessScheduledActions();
@@ -624,8 +624,7 @@ void Scheduler::ProcessScheduledActions() {
       case SchedulerStateMachine::ACTION_SEND_BEGIN_MAIN_FRAME:
         compositor_timing_history_->WillBeginMainFrame(
             begin_main_frame_args_.on_critical_path,
-            begin_main_frame_args_.frame_time,
-            begin_main_frame_args_.type);
+            begin_main_frame_args_.frame_time);
         state_machine_.WillSendBeginMainFrame();
         // TODO(brianderson): Pass begin_main_frame_args_ directly to client.
         client_->ScheduledActionSendBeginMainFrame(begin_main_frame_args_);