Allow Windows to use system Vsync if only one window is swapping

ui/gl/gl_surface.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_GL_GL_SURFACE_H_
 #define UI_GL_GL_SURFACE_H_
 
 #include <string>
 
 #include "base/callback.h"
@@ skipping 144 matching lines @@
   // Create a GL surface that renders directly to a view.
   static scoped_refptr<GLSurface> CreateViewGLSurface(
       gfx::AcceleratedWidget window);
 
   // Create a GL surface used for offscreen rendering.
   static scoped_refptr<GLSurface> CreateOffscreenGLSurface(
       const gfx::Size& size);
 
   static GLSurface* GetCurrent();
 
+  // Called when the swap interval for the associated context changes.
+  virtual void OnSetSwapInterval(int interval);
+
  protected:
   virtual ~GLSurface();
   static bool InitializeOneOffImplementation(GLImplementation impl,
                                              bool fallback_to_osmesa,
                                              bool gpu_service_logging,
                                              bool disable_gl_drawing);
   static bool InitializeOneOffInternal();
   static void SetCurrent(GLSurface* surface);
 
   static bool ExtensionsContain(const char* extensions, const char* name);
@@ skipping 51 matching lines @@
 
  private:
   scoped_refptr<GLSurface> surface_;
 
   DISALLOW_COPY_AND_ASSIGN(GLSurfaceAdapter);
 };
 
 }  // namespace gfx
 
 #endif  // UI_GL_GL_SURFACE_H_