Clean up threading around VR Scene updates.

chrome/browser/android/vr_shell/ui_scene.h

Index: chrome/browser/android/vr_shell/ui_scene.h
diff --git a/chrome/browser/android/vr_shell/ui_scene.h b/chrome/browser/android/vr_shell/ui_scene.h
index 5271f7b37959e4b39a5808160a0fb66c8af0ea25..d974fdf33a015b51121fe79197a10ab714292ce8 100644
--- a/chrome/browser/android/vr_shell/ui_scene.h
+++ b/chrome/browser/android/vr_shell/ui_scene.h
@@ -60,7 +60,8 @@ class UiScene {
   void UpdateTransforms(float screen_tilt, int64_t time_in_micro);
 
   // Handle a batch of commands passed from the UI HTML.
-  void HandleCommands(const base::ListValue* commands, int64_t time_in_micro);
+  void HandleCommands(std::unique_ptr<base::ListValue> commands,
+                      int64_t time_in_micro);
 
   const std::vector<std::unique_ptr<ContentRectangle>>& GetUiElements() const;
 
@@ -68,9 +69,6 @@ class UiScene {
 
   ContentRectangle* GetContentQuad();
 
-  // Return a monotonic time in microseconds for coordinating animations.
-  static int64_t TimeInMicroseconds();
-
  private:
   void ApplyRecursiveTransforms(const ContentRectangle& element,
                                 ReversibleTransform* transform);