Ack swap buffers after a timeout

content/browser/renderer_host/compositing_iosurface_layer_mac.h

Index: content/browser/renderer_host/compositing_iosurface_layer_mac.h
diff --git a/content/browser/renderer_host/compositing_iosurface_layer_mac.h b/content/browser/renderer_host/compositing_iosurface_layer_mac.h
index 9b1b6aa3f8d9cfdc56263894ab4812e8b140aedc..80a152dd35c0cb4b92161fe732f492f6415f3de4 100644
--- a/content/browser/renderer_host/compositing_iosurface_layer_mac.h
+++ b/content/browser/renderer_host/compositing_iosurface_layer_mac.h
@@ -9,15 +9,16 @@
 
 #include "base/mac/scoped_cftyperef.h"
 #include "base/memory/ref_counted.h"
+#include "base/timer/timer.h"
 
 namespace content {
 class CompositingIOSurfaceMac;
 class CompositingIOSurfaceContext;
+class CompositingIOSurfaceLayerHelper;
 
 class CompositingIOSurfaceLayerClient {
  public:
   virtual void AcceleratedLayerDidDrawFrame(bool succeeded) = 0;
-  virtual bool AcceleratedLayerHasNotAckedPendingFrame() const = 0;
 };
 
 }
@@ -29,11 +30,21 @@ class CompositingIOSurfaceLayerClient {
   scoped_refptr<content::CompositingIOSurfaceMac> iosurface_;
   scoped_refptr<content::CompositingIOSurfaceContext> context_;
 
+  // The browser places back-pressure on the GPU by not acknowledging swap
+  // calls until they appear on the screen. This can lead to hangs if the
+  // view is moved offscreen (among other things). Prevent hangs by always
+  // acknowledging the frame after timeout of 1/6th of a second  has passed.
+  scoped_ptr<content::CompositingIOSurfaceLayerHelper> helper_;
+  scoped_ptr<base::DelayTimer<content::CompositingIOSurfaceLayerHelper>> timer_;
+
   // Used to track when canDrawInCGLContext should return YES. This can be
   // in response to receiving a new compositor frame, or from any of the events
   // that cause setNeedsDisplay to be called on the layer.
   BOOL needs_display_;
 
+  // This is set when a frame is received, and un-set when the frame is drawn.
+  BOOL has_pending_frame_;
+
   // Incremented every time that this layer is asked to draw but does not have
   // new content to draw.
   uint64 did_not_draw_counter_;