Ozone: Avoid blocking in Swapbuffer Call.

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 1302cce4e5331b558a502e4311fac3a1ed7e529a..30e1fca1c6edff06cae615ca524b724d65f7a9bb 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"
@@ -128,6 +129,14 @@ class GL_EXPORT GLSurface : public base::RefCounted<GLSurface> {
 
   virtual bool IsSurfaceless() const;
 
+  typedef base::Callback<void()>
+      PageFlipCompletionCallback;
+  // On platforms where Chromium manages the system front/back buffer, we need
+  // to know when front buffer is actually displayed on screen. This
+  // callback should be called after the front buffer is displayed on screen.
+  virtual void SetPageFlipCompletionCallback(
+      const PageFlipCompletionCallback& callback);
+
   // Create a GL surface that renders directly to a view.
   static scoped_refptr<GLSurface> CreateViewGLSurface(
       gfx::AcceleratedWidget window);
@@ -189,6 +198,9 @@ class GL_EXPORT GLSurfaceAdapter : public GLSurface {
                             const RectF& crop_rect) override;
   bool IsSurfaceless() const override;
 
+  void SetPageFlipCompletionCallback(
+      const PageFlipCompletionCallback& callback) override;
+
   GLSurface* surface() const { return surface_.get(); }
 
  protected: