Clean up GPU back-pressure with remote CALayers

content/common/gpu/image_transport_surface_calayer_mac.h

Index: content/common/gpu/image_transport_surface_calayer_mac.h
diff --git a/content/common/gpu/image_transport_surface_calayer_mac.h b/content/common/gpu/image_transport_surface_calayer_mac.h
index 20ccce35cee59b5f0b79d692e0e115c32d49c1e1..a7584ff2370cf4fa1782d8b9b27679c4071c6985 100644
--- a/content/common/gpu/image_transport_surface_calayer_mac.h
+++ b/content/common/gpu/image_transport_surface_calayer_mac.h
@@ -31,7 +31,7 @@ class CALayerStorageProvider
   virtual void SwapBuffers(const gfx::Size& size, float scale_factor) override;
   virtual void WillWriteToBackbuffer() override;
   virtual void DiscardBackbuffer() override;
-  virtual void SwapBuffersAckedByBrowser() override;
+  virtual void SwapBuffersAckedByBrowser(bool disable_throttling) override;
 
   // Interface to ImageTransportLayer:
   CGLContextObj LayerShareGroupContext();
@@ -40,8 +40,11 @@ class CALayerStorageProvider
   void LayerResetStorageProvider();
 
  private:
-  void DrawWithVsyncDisabled();
-  void SendPendingSwapToBrowserAfterFrameDrawn();
+  void DrawImmediatelyAndUnblockBrowser();
+
+  // The browser will be blocked while there is a frame that was sent to it but
+  // hasn't drawn yet. This call will un-block the browser.
+  void UnblockBrowserIfNeeded();
 
   ImageTransportSurfaceFBO* transport_surface_;
 
@@ -49,9 +52,16 @@ class CALayerStorageProvider
   // animate.
   const bool gpu_vsync_disabled_;
 
+  // Used also to determine if we should wait for CoreAnimation to call our
+  // drawInCGLContext, or if we should force it with displayIfNeeded.
+  bool throttling_disabled_;
+
   // Set when a new swap occurs, and un-set when |layer_| draws that frame.
   bool has_pending_draw_;
 
+  // Weak factory against which a timeout task for forcing a draw is created.
+  base::WeakPtrFactory<CALayerStorageProvider> pending_draw_weak_factory_;

[piman, 2014/10/08 01:22:15]

Why not keep as last member? It's usually done to prevent access to destructed
fields if the weak ptr is dereferenced during teardown of those fields.

[ccameron, 2014/10/08 18:44:00]

Moved back (thought to put it next to pending_draw, which it is logically paired
with, but yeah, the end is better).

+
   // A counter that is incremented whenever LayerCanDraw returns false. If this
   // reaches a threshold, then |layer_| is switched to synchronous drawing to
   // save CPU work.
@@ -68,7 +78,6 @@ class CALayerStorageProvider
   base::scoped_nsobject<CAContext> context_;
   base::scoped_nsobject<ImageTransportLayer> layer_;
 
-  base::WeakPtrFactory<CALayerStorageProvider> weak_factory_;
   DISALLOW_COPY_AND_ASSIGN(CALayerStorageProvider);
 };