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

ui/gl/gl_surface_egl.h

Index: ui/gl/gl_surface_egl.h
diff --git a/ui/gl/gl_surface_egl.h b/ui/gl/gl_surface_egl.h
index 952ccad49e5880970581d5a1db53df205b92eb21..789b234d659b141c8130faea96a19ee0a6c5373a 100644
--- a/ui/gl/gl_surface_egl.h
+++ b/ui/gl/gl_surface_egl.h
@@ -82,6 +82,8 @@ class GL_EXPORT NativeViewGLSurfaceEGL : public GLSurfaceEGL {
 
   EGLNativeWindowType window_;
 
+  virtual void SetSwapInterval(int interval) override;
+
  private:
   EGLSurface surface_;
   bool supports_post_sub_buffer_;
@@ -90,6 +92,16 @@ class GL_EXPORT NativeViewGLSurfaceEGL : public GLSurfaceEGL {
 
   scoped_ptr<VSyncProvider> vsync_provider_;
 
+  int swap_interval_;
+  bool vsync_override_;
+
+#if defined(OS_WIN)
+  unsigned int swap_generation_;
+  static unsigned int current_swap_generation_;
+  static unsigned int swaps_this_generation_;
+  static unsigned int last_multiswap_generation_;
+#endif
+
   DISALLOW_COPY_AND_ASSIGN(NativeViewGLSurfaceEGL);
 };