Bug 1435022 - Clean up GetLastComposeTime. r=sotaro

MozReview-Commit-ID: CEaz01FyjSs

--HG--
extra : rebase_source : 44c92477f6374764e084249bae74639c3706b5c0

gfx/layers/ipc/CompositorVsyncScheduler.cpp

@@ -334,5 +334,12 @@ CompositorVsyncScheduler::ScheduleTask(already_AddRefed<CancelableRunnable> aTas
   CompositorThreadHolder::Loop()->PostDelayedTask(Move(aTask), 0);
 }
 
+const TimeStamp&
+CompositorVsyncScheduler::GetLastComposeTime() const
+{
+  MOZ_ASSERT(CompositorThreadHolder::IsInCompositorThread());
+  return mLastCompose;
+}
+
 } // namespace layers
 } // namespace mozilla

gfx/layers/ipc/CompositorVsyncScheduler.h

@@ -83,11 +83,11 @@ public:
    */
   void ForceComposeToTarget(gfx::DrawTarget* aTarget, const gfx::IntRect* aRect);
 
-  const TimeStamp& GetLastComposeTime()
-  {
-    return mLastCompose;
-  }
-
+  /**
+   * Return the vsync timestamp of the last or ongoing composite. Must be called
+   * on the compositor thread.
+   */
+  const TimeStamp& GetLastComposeTime() const;
 #ifdef COMPOSITOR_PERFORMANCE_WARNING
   const TimeStamp& GetExpectedComposeStartTime()
   {