Use black for resize gutter in tab fullscreen mode.

content/browser/renderer_host/render_widget_host_view_aura.cc

Index: content/browser/renderer_host/render_widget_host_view_aura.cc
diff --git a/content/browser/renderer_host/render_widget_host_view_aura.cc b/content/browser/renderer_host/render_widget_host_view_aura.cc
index c4f7a90aa6b8e4e29a02767416b775d567fd60d7..0839a59c3fda01b1894cb156ae9a95ec3a27f091 100644
--- a/content/browser/renderer_host/render_widget_host_view_aura.cc
+++ b/content/browser/renderer_host/render_widget_host_view_aura.cc
@@ -2849,6 +2849,15 @@ bool RenderWidgetHostViewAura::DelegatedFrameHostIsVisible() const {
   return !host_->is_hidden();
 }
 
+void RenderWidgetHostViewAura::DelegatedFrameHostOverrideGutterColor(
+    SkColor* color) 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

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

Doesn't this make a black flash if the page is white, instead of just having the
white background spread everywhere and then the content re-layouts on top of it?

+  // gutter color.
+  if (host_->delegate()->IsFullscreenForCurrentTab(host_))
+    *color = SK_ColorBLACK;
+}
+
 gfx::Size RenderWidgetHostViewAura::DelegatedFrameHostDesiredSizeInDIP() const {
   return window_->bounds().size();
 }