cc: Track BeginMainFrame more precisely in CompositorTimingHistory.

cc/scheduler/scheduler_state_machine_unittest.cc

Index: cc/scheduler/scheduler_state_machine_unittest.cc
diff --git a/cc/scheduler/scheduler_state_machine_unittest.cc b/cc/scheduler/scheduler_state_machine_unittest.cc
index 20e8188584d84c37ca4d2cac3b0c50d98c140ea7..fcd4516594cec97fe1f4ad0716bfc5b6150926f4 100644
--- a/cc/scheduler/scheduler_state_machine_unittest.cc
+++ b/cc/scheduler/scheduler_state_machine_unittest.cc
@@ -1233,6 +1233,7 @@ TEST(SchedulerStateMachineTest, TestAbortBeginMainFrameBecauseInvisible) {
 
   // Become invisible and abort BeginMainFrame.
   state.SetVisible(false);
+  state.NotifyBeginMainFrameStarted();
   state.BeginMainFrameAborted(CommitEarlyOutReason::ABORTED_NOT_VISIBLE);
 
   // NeedsCommit should now be true again because we never actually did a
@@ -1288,6 +1289,7 @@ TEST(SchedulerStateMachineTest, TestAbortBeginMainFrameBecauseCommitNotNeeded) {
 
   // Abort the commit, true means that the BeginMainFrame was sent but there
   // was no work to do on the main thread.
+  state.NotifyBeginMainFrameStarted();
   state.BeginMainFrameAborted(CommitEarlyOutReason::FINISHED_NO_UPDATES);
 
   // NeedsCommit should now be false because the commit was actually handled.
@@ -1849,6 +1851,7 @@ TEST(SchedulerStateMachineTest,
 
   // Since only the scroll offset changed, the main thread will abort the
   // commit.
+  state.NotifyBeginMainFrameStarted();
   state.BeginMainFrameAborted(CommitEarlyOutReason::FINISHED_NO_UPDATES);
 
   // Since the commit was aborted, we should draw right away instead of waiting