Add callback when queueing frame on Surface to create backpressure.

cc/surfaces/surface.h

Index: cc/surfaces/surface.h
diff --git a/cc/surfaces/surface.h b/cc/surfaces/surface.h
index 403d2e56baf6f8a575509050152fb4bc90bccbc8..ca4626f16413c223ed1485b3e459f81b6b325d6b 100644
--- a/cc/surfaces/surface.h
+++ b/cc/surfaces/surface.h
@@ -5,6 +5,7 @@
 #ifndef CC_SURFACES_SURFACE_H_
 #define CC_SURFACES_SURFACE_H_
 
+#include "base/callback_forward.h"
 #include "base/containers/hash_tables.h"
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
@@ -30,6 +31,9 @@ class CC_SURFACES_EXPORT Surface {
   // Returns the most recent frame that is eligible to be rendered.
   const CompositorFrame* GetEligibleFrame();
 
+  void AddDrawCallback(const base::Closure& closure);
+  void RunDrawCallbacks();
+
   SurfaceFactory* factory() { return factory_; }
 
  private:
@@ -39,6 +43,8 @@ class CC_SURFACES_EXPORT Surface {
   // TODO(jamesr): Support multiple frames in flight.
   scoped_ptr<CompositorFrame> current_frame_;
 
+  std::vector<base::Closure> draw_callbacks_;

[jamesr, 2014/08/22 06:00:12]

a surface can only have one active frame at any point in time (it can have more
queued, but not active), so why does it need a vector of draw callbacks?

+
   DISALLOW_COPY_AND_ASSIGN(Surface);
 };