VR: Split off UI code into a library to ease future unit testing.

chrome/browser/android/vr_shell/ui_elements/screen_dimmer.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_UI_ELEMENTS_SCREEN_DIMMER_H_
 #define CHROME_BROWSER_ANDROID_VR_SHELL_UI_ELEMENTS_SCREEN_DIMMER_H_
 
 #include "base/macros.h"
 #include "chrome/browser/android/vr_shell/ui_elements/ui_element.h"
 
 namespace vr_shell {
 
 class ScreenDimmer : public UiElement {
  public:
   ScreenDimmer();
   ~ScreenDimmer() override;
 
   void Initialize() final;
 
   // UiElement interface.
-  void Render(VrShellRenderer* renderer,
+  void Render(UiElementRenderer* renderer,
               vr::Mat4f view_proj_matrix) const final;
 
   DISALLOW_COPY_AND_ASSIGN(ScreenDimmer);
 };
 
 }  // namespace vr_shell
 
 #endif  // CHROME_BROWSER_ANDROID_VR_SHELL_UI_ELEMENTS_SCREEN_DIMMER_H_