Use black for resize gutter in tab fullscreen mode.

content/browser/renderer_host/delegated_frame_host.cc

 // Copyright 2014 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 "content/browser/renderer_host/delegated_frame_host.h"
 
 #include <algorithm>
 #include <string>
 #include <utility>
 #include <vector>
@@ skipping 238 matching lines @@
 
 void DelegatedFrameHost::WasResized() {
   if (client_->DelegatedFrameHostDesiredSizeInDIP() !=
           current_frame_size_in_dip_ &&
       !client_->DelegatedFrameHostIsVisible())
     EvictDelegatedFrame();
   MaybeCreateResizeLock();
   UpdateGutters();
 }
 
+SkColor DelegatedFrameHost::GetGutterColor() const {
+  // In fullscreen mode resizing is uncommon, so it makes more sense to
+  // make the initial switch to fullscreen mode look better by using black as
+  // the gutter color.
+  SkColor color = background_color_;
+  client_->DelegatedFrameHostOverrideGutterColor(&color);

[danakj, 2016/04/25 22:17:58]

nit: i think maybe passing the color and returning a possibly-changed color is a
bit nicer and may produce nicer codegen? no pointers, RVO, etc.

then this would be

return client_->DFHGetGutterColor(color);

+  return color;
+}
+
 void DelegatedFrameHost::UpdateGutters() {
   if (surface_id_.is_null()) {
     right_gutter_.reset();
     bottom_gutter_.reset();
     return;
   }
+
   if (current_frame_size_in_dip_.width() <
       client_->DelegatedFrameHostDesiredSizeInDIP().width()) {
     right_gutter_.reset(new ui::Layer(ui::LAYER_SOLID_COLOR));
-    right_gutter_->SetColor(background_color_);
+    right_gutter_->SetColor(GetGutterColor());
     int width = client_->DelegatedFrameHostDesiredSizeInDIP().width() -
                 current_frame_size_in_dip_.width();
     // The right gutter also includes the bottom-right corner, if necessary.
     int height = client_->DelegatedFrameHostDesiredSizeInDIP().height();
     right_gutter_->SetBounds(
         gfx::Rect(current_frame_size_in_dip_.width(), 0, width, height));
 
     client_->DelegatedFrameHostGetLayer()->Add(right_gutter_.get());
   } else {
     right_gutter_.reset();
   }
 
   if (current_frame_size_in_dip_.height() <
       client_->DelegatedFrameHostDesiredSizeInDIP().height()) {
     bottom_gutter_.reset(new ui::Layer(ui::LAYER_SOLID_COLOR));
-    bottom_gutter_->SetColor(background_color_);
+    bottom_gutter_->SetColor(GetGutterColor());
     int width = current_frame_size_in_dip_.width();
     int height = client_->DelegatedFrameHostDesiredSizeInDIP().height() -
                  current_frame_size_in_dip_.height();
     bottom_gutter_->SetBounds(
         gfx::Rect(0, current_frame_size_in_dip_.height(), width, height));
     client_->DelegatedFrameHostGetLayer()->Add(bottom_gutter_.get());
 
   } else {
     bottom_gutter_.reset();
   }
@@ skipping 588 matching lines @@
     cc::SurfaceManager* manager = factory->GetSurfaceManager();
     new_layer->SetShowSurface(
         surface_id_, base::Bind(&SatisfyCallback, base::Unretained(manager)),
         base::Bind(&RequireCallback, base::Unretained(manager)),
         current_surface_size_, current_scale_factor_,
         current_frame_size_in_dip_);
   }
 }
 
 }  // namespace content