gpu: Early return GpuCommandBufferStub::OnWaitSyncPoint() if the sync point is retired.

content/common/gpu/sync_point_manager.h

Index: content/common/gpu/sync_point_manager.h
diff --git a/content/common/gpu/sync_point_manager.h b/content/common/gpu/sync_point_manager.h
index 04591828bf757cc298b96e2a8fc522a336243271..d46ad609073b15524b429b8548fa333960d6705f 100644
--- a/content/common/gpu/sync_point_manager.h
+++ b/content/common/gpu/sync_point_manager.h
@@ -35,6 +35,8 @@ class SyncPointManager : public base::RefCountedThreadSafe<SyncPointManager> {
   // called on the main thread.
   void AddSyncPointCallback(uint32 sync_point, const base::Closure& callback);
 
+  bool IsSyncPointRetired(uint32 sync_point);
+
  private:
   friend class base::RefCountedThreadSafe<SyncPointManager>;
   typedef std::vector<base::Closure> ClosureList;