Mac: Fix flickering while entering/leaving fullscreen low power video

ui/accelerated_widget_mac/ca_layer_tree_coordinator.h

 // Copyright 2016 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_ACCELERATED_WIDGET_MAC_CA_LAYER_TREE_HOST_H_
 #define UI_ACCELERATED_WIDGET_MAC_CA_LAYER_TREE_HOST_H_
 
 #include "ui/accelerated_widget_mac/accelerated_widget_mac_export.h"
 #include "ui/accelerated_widget_mac/ca_renderer_layer_tree.h"
 #include "ui/accelerated_widget_mac/gl_renderer_layer_tree.h"
@@ skipping 55 matching lines @@
   base::scoped_nsobject<AVSampleBufferDisplayLayer> fullscreen_low_power_layer_;
 
   // Frame that has been scheduled, but has not had a subsequent commit call
   // made yet.
   std::unique_ptr<GLRendererLayerTree> pending_gl_renderer_layer_tree_;
   std::unique_ptr<CARendererLayerTree> pending_ca_renderer_layer_tree_;
 
   // Frame that is currently being displayed on the screen.
   std::unique_ptr<GLRendererLayerTree> current_gl_renderer_layer_tree_;
   std::unique_ptr<CARendererLayerTree> current_ca_renderer_layer_tree_;
-  bool current_fullscreen_low_power_layer_valid_ = false;
+
+  // The number of frames since we used the low power layer. Used to avoid
+  // flashes during transitions between windows.
+  uint64_t frames_since_low_power_layer_was_valid_ = 0;
 
   DISALLOW_COPY_AND_ASSIGN(CALayerTreeCoordinator);
 };
 
 }  // namespace ui
 
 #endif  // UI_ACCELERATED_WIDGET_MAC_CA_LAYER_TREE_HOST_H_