[VrShell] Centralize color handling and enable close button on fullscreen

chrome/browser/android/vr_shell/textures/button_texture.cc

 // Copyright 2017 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 "chrome/browser/android/vr_shell/textures/button_texture.h"
 
 namespace vr_shell {
 
 ButtonTexture::ButtonTexture() = default;
 
 ButtonTexture::~ButtonTexture() = default;
 
+void ButtonTexture::OnSetMode() {
+  set_dirty();
+}
+
 void ButtonTexture::SetPressed(bool pressed) {
   if (pressed_ != pressed)
     set_dirty();
   pressed_ = pressed;
 }
 
 void ButtonTexture::SetHovered(bool hovered) {
   if (hovered_ != hovered)
     set_dirty();
   hovered_ = hovered;
 }
 
 }  // namespace vr_shell