Bug 1435022 - Inline OnForceComposeToTarget and clarify the comment. …

…r=sotaro

This function has only one call site and there's no need to make it
public.

MozReview-Commit-ID: 5o7B9KMyVqy

--HG--
extra : rebase_source : 38a915c19d48784ce086ebecd66b9f872ae03327

gfx/layers/ipc/CompositorVsyncScheduler.cpp

@@ -289,27 +289,27 @@ CompositorVsyncScheduler::Composite(TimeStamp aVsyncTimestamp)
 }
 
 void
-CompositorVsyncScheduler::OnForceComposeToTarget()
+CompositorVsyncScheduler::ForceComposeToTarget(gfx::DrawTarget* aTarget, const IntRect* aRect)
 {
+  MOZ_ASSERT(CompositorThreadHolder::IsInCompositorThread());
+
   /**
-   * bug 1138502 - There are cases such as during long-running window resizing events
-   * where we receive many sync RecvFlushComposites. We also get vsync notifications which
-   * will increment mVsyncNotificationsSkipped because a composite just occurred. After
-   * enough vsyncs and RecvFlushComposites occurred, we will disable vsync. Then at the next
-   * ScheduleComposite, we will enable vsync, then get a RecvFlushComposite, which will
-   * force us to unobserve vsync again. On some platforms, enabling/disabling vsync is not
-   * free and this oscillating behavior causes a performance hit. In order to avoid this problem,
-   * we reset the mVsyncNotificationsSkipped counter to keep vsync enabled.
+   * bug 1138502 - There are cases such as during long-running window resizing
+   * events where we receive many force-composites. We also continue to get
+   * vsync notifications. Because the force-composites trigger compositing and
+   * clear the mNeedsComposite counter, the vsync notifications will not need
+   * to do anything and so will increment the mVsyncNotificationsSkipped counter
+   * to indicate the vsync was ignored. If this happens enough times, we will
+   * disable listening for vsync entirely. On the next force-composite we will
+   * enable listening for vsync again, and continued force-composites and vsyncs
+   * will cause oscillation between observing vsync and not.
+   * On some platforms, enabling/disabling vsync is not free and this
+   * oscillating behavior causes a performance hit. In order to avoid this
+   * problem, we reset the mVsyncNotificationsSkipped counter to keep vsync
+   * enabled.
    */
-  MOZ_ASSERT(CompositorThreadHolder::IsInCompositorThread());
   mVsyncNotificationsSkipped = 0;
-}
 
-void
-CompositorVsyncScheduler::ForceComposeToTarget(gfx::DrawTarget* aTarget, const IntRect* aRect)
-{
-  MOZ_ASSERT(CompositorThreadHolder::IsInCompositorThread());
-  OnForceComposeToTarget();
   mLastCompose = TimeStamp::Now();
   ComposeToTarget(aTarget, aRect);
 }

gfx/layers/ipc/CompositorVsyncScheduler.h

@@ -50,7 +50,6 @@ class CompositorVsyncScheduler
 
   bool NotifyVsync(TimeStamp aVsyncTimestamp);
   void SetNeedsComposite();
-  void OnForceComposeToTarget();
 
   void ScheduleTask(already_AddRefed<CancelableRunnable>, int);
   void ResumeComposition();