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

ui/gl/gl_surface_egl.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_EGL_H_
 #define UI_GL_GL_SURFACE_EGL_H_
 
 #if defined(OS_WIN)
 #include <windows.h>
 #endif
@@ skipping 64 matching lines @@
 
   // Create a NativeViewGLSurfaceEGL with an externally provided VSyncProvider.
   // Takes ownership of the VSyncProvider.
   virtual bool Initialize(scoped_ptr<VSyncProvider> sync_provider);
 
  protected:
   ~NativeViewGLSurfaceEGL() override;
 
   EGLNativeWindowType window_;
 
+  virtual void SetSwapInterval(int interval) override;
+
  private:
   EGLSurface surface_;
   bool supports_post_sub_buffer_;
   EGLConfig config_;
   gfx::Size size_;
 
   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);
 };
 
 // Encapsulates a pbuffer EGL surface.
 class GL_EXPORT PbufferGLSurfaceEGL : public GLSurfaceEGL {
  public:
   explicit PbufferGLSurfaceEGL(const gfx::Size& size);
 
   // Implement GLSurface.
   EGLConfig GetConfig() override;
@@ skipping 39 matching lines @@
   ~SurfacelessEGL() override;
 
  private:
   gfx::Size size_;
   DISALLOW_COPY_AND_ASSIGN(SurfacelessEGL);
 };
 
 }  // namespace gfx
 
 #endif  // UI_GL_GL_SURFACE_EGL_H_