cc: VideoResourceUpdater: don't dismiss the sync_point given by the compositor

cc/resources/video_resource_updater.cc

Index: cc/resources/video_resource_updater.cc
diff --git a/cc/resources/video_resource_updater.cc b/cc/resources/video_resource_updater.cc
index c0d6923fcf11724b20d5a06714a14862bbec59d5..ce6bee043d3a94a7762370b3139fea119545dab1 100644
--- a/cc/resources/video_resource_updater.cc
+++ b/cc/resources/video_resource_updater.cc
@@ -27,15 +27,18 @@ const ResourceFormat kRGBResourceFormat = RGBA_8888;
 
 class SyncPointClientImpl : public media::VideoFrame::SyncPointClient {
  public:
-  explicit SyncPointClientImpl(gpu::gles2::GLES2Interface* gl) : gl_(gl) {}
+  explicit SyncPointClientImpl(gpu::gles2::GLES2Interface* gl,
+                               uint32 sync_point)
+      : gl_(gl), sync_point_(sync_point) {}
   ~SyncPointClientImpl() override {}
-  uint32 InsertSyncPoint() override { return gl_->InsertSyncPointCHROMIUM(); }
+  uint32 InsertSyncPoint() override { return sync_point_; }
   void WaitSyncPoint(uint32 sync_point) override {
     gl_->WaitSyncPointCHROMIUM(sync_point);
   }
 
  private:
   gpu::gles2::GLES2Interface* gl_;
+  uint32 sync_point_;
 };
 
 }  // namespace
@@ -378,7 +381,8 @@ void VideoResourceUpdater::ReturnTexture(
   // VideoFrame::UpdateReleaseSyncPoint() creates new sync point using the same

[danakj, 2015/04/14 15:56:27]

What about this comment? Why is it wrong?

[llandwerlin-old, 2015/04/14 16:21:54]

Thanks, I will update the comment.

It's wrong because prior to https://codereview.chromium.org/312803002/ we kept
adding sync points to the media::VideoFrame.

If we want to keep only one sync point, we need to build up a chain of
dependency. We can do this by inserting a WaitSyncPointCHROMIUM op in the
command stream and create a new sync point to be used by the media::VideoFrame,
but since we do not draw with the GL texture from the renderer, we can directly
replace the sync point inside the media::VideoFrame.

   // GL context which created the given |sync_point|, so discard the
   // |sync_point|.
-  SyncPointClientImpl client(updater->context_provider_->ContextGL());
+  SyncPointClientImpl client(updater->context_provider_->ContextGL(),
+                             sync_point);
   video_frame->UpdateReleaseSyncPoint(&client);
 }