Migrate WebGL contexts on backgrounded tabs to the integrated GPU.

ui/gl/gl_context_cgl.h

Index: ui/gl/gl_context_cgl.h
diff --git a/ui/gl/gl_context_cgl.h b/ui/gl/gl_context_cgl.h
index 72fbb4d6c8cf92b3d659a199ac5b735710d6cb18..5694effc931df6f9162e28ea0f19a67ebd8271da 100644
--- a/ui/gl/gl_context_cgl.h
+++ b/ui/gl/gl_context_cgl.h
@@ -33,6 +33,7 @@ class GL_EXPORT GLContextCGL : public GLContextReal {
   void SetSafeToForceGpuSwitch() override;
   bool ForceGpuSwitchIfNeeded() override;
   YUVToRGBConverter* GetYUVToRGBConverter() override;
+  void SetPerformancePreference(GpuPerformancePreference pref) override;
 
  protected:
   ~GLContextCGL() override;
@@ -41,6 +42,9 @@ class GL_EXPORT GLContextCGL : public GLContextReal {
   void Destroy();
   GpuPreference GetGpuPreference();
 
+  bool AllocateDiscretePixelFormat();
+  void ReleaseDiscretePixelFormat();
+
   void* context_;
   GpuPreference gpu_preference_;
   std::unique_ptr<YUVToRGBConverter> yuv_to_rgb_converter_;