Ozone: Avoid blocking in Swapbuffer Call.

ui/ozone/public/surface_ozone_egl.h

Index: ui/ozone/public/surface_ozone_egl.h
diff --git a/ui/ozone/public/surface_ozone_egl.h b/ui/ozone/public/surface_ozone_egl.h
index 4f38f06b2117c2e2605af9bd2f86d1f4c92a871c..d3cab531e407848f3a9f61aba0ec7eca9299611c 100644
--- a/ui/ozone/public/surface_ozone_egl.h
+++ b/ui/ozone/public/surface_ozone_egl.h
@@ -6,6 +6,7 @@
 #define UI_OZONE_PUBLIC_SURFACE_OZONE_EGL_H_
 
 #include "base/basictypes.h"
+#include "base/callback.h"
 #include "base/memory/scoped_ptr.h"
 #include "ui/gfx/overlay_transform.h"
 #include "ui/ozone/ozone_base_export.h"
@@ -38,6 +39,15 @@ class OZONE_BASE_EXPORT SurfaceOzoneEGL {
   // be used to present the new front buffer if the platform requires this.
   virtual bool OnSwapBuffers() = 0;
 
+  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.
+  // This should be a noop on platforms where these buffers are managed by an
+  // external window system.
+  virtual void SetPageFlipCompletionCallback(
+      const PageFlipCompletionCallback& callback) = 0;
+
   // Returns a gfx::VsyncProvider for this surface. Note that this may be
   // called after we have entered the sandbox so if there are operations (e.g.
   // opening a file descriptor providing vsync events) that must be done