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

ui/accelerated_widget_mac/ca_layer_tree_coordinator.mm

 // 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.
 
 #include "ui/accelerated_widget_mac/ca_layer_tree_coordinator.h"
 
 #include <AVFoundation/AVFoundation.h>
 
 #include "base/mac/mac_util.h"
 #include "base/trace_event/trace_event.h"
 #include "ui/base/cocoa/animation_utils.h"
 
 namespace ui {
 
+namespace {
+const uint64_t kFramesBeforeFlushingLowPowerLayer = 15;
+}
+
 CALayerTreeCoordinator::CALayerTreeCoordinator(
     bool allow_remote_layers,
     bool allow_av_sample_buffer_display_layer)
     : allow_remote_layers_(allow_remote_layers),
       allow_av_sample_buffer_display_layer_(
           allow_av_sample_buffer_display_layer) {
   if (allow_remote_layers_) {
     root_ca_layer_.reset([[CALayer alloc] init]);
     [root_ca_layer_ setGeometryFlipped:YES];
     [root_ca_layer_ setOpaque:YES];
@@ skipping 64 matching lines @@
         scale_factor_, pixel_damage_rect);
     current_gl_renderer_layer_tree_.swap(pending_gl_renderer_layer_tree_);
     current_ca_renderer_layer_tree_.reset();
   } else {
     TRACE_EVENT0("gpu", "Blank frame: No overlays or CALayers");
     [root_ca_layer_ setSublayers:nil];
     current_gl_renderer_layer_tree_.reset();
     current_ca_renderer_layer_tree_.reset();
   }
 
-  // TODO(ccameron): It may be necessary to leave the last image up for a few
-  // extra frames to allow a smooth switch between the normal and low-power
-  // NSWindows.
-  if (current_fullscreen_low_power_layer_valid_ &&
-      !*fullscreen_low_power_layer_valid) {
+  // It is necessary to leave the last image up for a few extra frames to allow
+  // a smooth switch between the normal and low-power NSWindows.
+  if (*fullscreen_low_power_layer_valid)
+    frames_since_low_power_layer_was_valid_ = 0;
+  else
+    frames_since_low_power_layer_was_valid_ += 1;
+  if (frames_since_low_power_layer_was_valid_ ==
+      kFramesBeforeFlushingLowPowerLayer)
     [fullscreen_low_power_layer_ flushAndRemoveImage];
-  }
-  current_fullscreen_low_power_layer_valid_ = *fullscreen_low_power_layer_valid;
 
   // Reset all state for the next frame.
   pending_ca_renderer_layer_tree_.reset();
   pending_gl_renderer_layer_tree_.reset();
 }
 
 CALayer* CALayerTreeCoordinator::GetCALayerForDisplay() const {
   DCHECK(allow_remote_layers_);
   return root_ca_layer_.get();
 }
 
 CALayer* CALayerTreeCoordinator::GetFullscreenLowPowerLayerForDisplay() const {
   return fullscreen_low_power_layer_.get();
 }
 
 IOSurfaceRef CALayerTreeCoordinator::GetIOSurfaceForDisplay() {
   DCHECK(!allow_remote_layers_);
   if (!current_gl_renderer_layer_tree_)
     return nullptr;
   return current_gl_renderer_layer_tree_->RootLayerIOSurface();
 }
 
 }  // namespace ui