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

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

 // 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.
 
 #ifndef CHROME_BROWSER_ANDROID_VR_SHELL_TEXTURES_BUTTON_TEXTURE_H_
 #define CHROME_BROWSER_ANDROID_VR_SHELL_TEXTURES_BUTTON_TEXTURE_H_
 
 #include "chrome/browser/android/vr_shell/textures/ui_texture.h"
 
 namespace vr_shell {
 
 class ButtonTexture : public UiTexture {
  public:
   ButtonTexture();
   ~ButtonTexture() override;
 
   void SetPressed(bool pressed);
   bool pressed() const { return pressed_; }
 
   void SetHovered(bool hovered);
   bool hovered() const { return hovered_; }
 
  private:
+  void OnSetMode() override;
   bool pressed_ = false;
   bool hovered_ = false;
 };
 
 }  // namespace vr_shell
 
 #endif  // CHROME_BROWSER_ANDROID_VR_SHELL_TEXTURES_BUTTON_TEXTURE_H_