Add support to delay sending SwapbufferAck as needed.

ui/gl/gl_surface.h

Index: ui/gl/gl_surface.h
diff --git a/ui/gl/gl_surface.h b/ui/gl/gl_surface.h
index ec04c9626dab43a7c4565846909cf17eadcf0324..744ec069fbe8fc0090b7c9454fe7a9614b8036dd 100644
--- a/ui/gl/gl_surface.h
+++ b/ui/gl/gl_surface.h
@@ -7,6 +7,7 @@
 
 #include <string>
 
+#include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "build/build_config.h"
 #include "ui/gfx/native_widget_types.h"
@@ -72,9 +73,27 @@ class GL_EXPORT GLSurface : public base::RefCounted<GLSurface> {
   // FBO. Otherwise returns 0.
   virtual unsigned int GetBackingFrameBufferObject();
 
+  typedef base::Callback<void()> SwapCompletionCallback;
+  // Swaps front and back buffers. This has no effect for off-screen
+  // contexts. On some platforms, we want to send SwapBufferAck only after the
+  // surface is displayed on screen. The callback can be used to delay sending
+  // SwapBufferAck till that data is available. The callback should be run on
+  // GPUMainThread only.

[piman, 2014/12/22 20:53:15]

nit: in ui/gl there's no notion of GpuMainThread.
I would phrase it as: the callback should be run on the calling thread (i.e.
same thread SwapBuffersAsync is called).

[kalyank, 2014/12/23 11:22:42]

Done.

+  virtual bool SwapBuffersAsync(const SwapCompletionCallback& callback);
+
   // Copy part of the backbuffer to the frontbuffer.
   virtual bool PostSubBuffer(int x, int y, int width, int height);
 
+  // Copy part of the backbuffer to the frontbuffer. On some platforms, we want
+  // to send SwapBufferAck only after the surface is displayed on screen. The
+  // callback can be used to delay sending SwapBufferAck till that data is
+  // available. The callback should be run on GPUMainThread only.
+  virtual bool PostSubBufferAsync(int x,
+                                  int y,
+                                  int width,
+                                  int height,
+                                  const SwapCompletionCallback& callback);
+
   // Initialize GL bindings.
   static bool InitializeOneOff();
 
@@ -173,7 +192,13 @@ class GL_EXPORT GLSurfaceAdapter : public GLSurface {
   bool DeferDraws() override;
   bool IsOffscreen() override;
   bool SwapBuffers() override;
+  bool SwapBuffersAsync(const SwapCompletionCallback& callback) override;
   bool PostSubBuffer(int x, int y, int width, int height) override;
+  bool PostSubBufferAsync(int x,
+                          int y,
+                          int width,
+                          int height,
+                          const SwapCompletionCallback& callback) override;
   bool SupportsPostSubBuffer() override;
   gfx::Size GetSize() override;
   void* GetHandle() override;