VrShell: Allow native control of UI element opacity.

chrome/browser/android/vr_shell/ui_elements.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_ELEMENTS_H_
 #define CHROME_BROWSER_ANDROID_VR_SHELL_UI_ELEMENTS_H_
 
 #include <memory>
 #include <vector>
 
@@ skipping 82 matching lines @@
   // The scale of the object, and its children.
   gvr::Vec3f scale = {1.0f, 1.0f, 1.0f};
 
   // The rotation of the object, and its children.
   RotationAxisAngle rotation = {1.0f, 0.0f, 0.0f, 0.0f};
 
   // The translation of the object, and its children.  Translation is applied
   // after rotation and scaling.
   gvr::Vec3f translation = {0.0f, 0.0f, 0.0f};
 
+  // The opacity of the object (between 0.0 and 1.0).
+  float opacity = 1.0f;
+
+  // The computed opacity, incorporating opacity of parent objects.
+  float computed_opacity;
+
   // If anchoring is specified, the translation will be relative to the
   // specified edge(s) of the parent, rather than the center.  A parent object
   // must be specified when using anchoring.
   XAnchoring x_anchoring = XAnchoring::XNONE;
   YAnchoring y_anchoring = YAnchoring::YNONE;
 
   // Animations that affect the properties of the object over time.
   std::vector<std::unique_ptr<Animation>> animations;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ContentRectangle);
 };
 
 }  // namespace vr_shell
 
 #endif  // CHROME_BROWSER_ANDROID_VR_SHELL_UI_ELEMENTS_H_