cc: Track BeginMainFrame more precisely in CompositorTimingHistory.

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 aeda6dd6ede35a17456201bf6ea55234be1ba611..f0b0f2c96d17e88cf0c6c9cc99245c7c136c2ab0 100644
--- a/cc/scheduler/scheduler_state_machine.cc
+++ b/cc/scheduler/scheduler_state_machine.cc
@@ -1025,7 +1025,7 @@ void SchedulerStateMachine::SetNeedsBeginMainFrame() {
 }
 
 void SchedulerStateMachine::NotifyReadyToCommit() {
-  DCHECK(begin_main_frame_state_ == BEGIN_MAIN_FRAME_STATE_STARTED)
+  DCHECK_EQ(begin_main_frame_state_, BEGIN_MAIN_FRAME_STATE_STARTED)
       << AsValue()->ToString();
   begin_main_frame_state_ = BEGIN_MAIN_FRAME_STATE_READY_TO_COMMIT;
   // In commit_to_active_tree mode, commit should happen right after
@@ -1036,7 +1036,7 @@ void SchedulerStateMachine::NotifyReadyToCommit() {
 }
 
 void SchedulerStateMachine::BeginMainFrameAborted(CommitEarlyOutReason reason) {
-  DCHECK_EQ(begin_main_frame_state_, BEGIN_MAIN_FRAME_STATE_SENT);
+  DCHECK_EQ(begin_main_frame_state_, BEGIN_MAIN_FRAME_STATE_STARTED);
   switch (reason) {
     case CommitEarlyOutReason::ABORTED_OUTPUT_SURFACE_LOST:
     case CommitEarlyOutReason::ABORTED_NOT_VISIBLE: