VrShell: Allow native control of UI element opacity.

chrome/browser/android/vr_shell/ui_scene.h

 // Copyright 2016 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_SCENE_H_
 #define CHROME_BROWSER_ANDROID_VR_SHELL_UI_SCENE_H_
 
 #include <memory>
 #include <vector>
 
@@ skipping 53 matching lines @@
                       int64_t time_in_micro);
 
   const std::vector<std::unique_ptr<ContentRectangle>>& GetUiElements() const;
 
   ContentRectangle* GetUiElementById(int element_id);
 
   ContentRectangle* GetContentQuad();
 
  private:
   void ApplyRecursiveTransforms(const ContentRectangle& element,
-                                ReversibleTransform* transform);
+                                ReversibleTransform* transform,
+                                float* opacity);
   void ApplyDictToElement(const base::DictionaryValue& dict,
                           ContentRectangle *element);
 
   std::vector<std::unique_ptr<ContentRectangle>> ui_elements_;
   ContentRectangle* content_element_ = nullptr;
 
   DISALLOW_COPY_AND_ASSIGN(UiScene);
 };
 
 }  // namespace vr_shell
 
 #endif  // CHROME_BROWSER_ANDROID_VR_SHELL_UI_SCENE_H_