Clean up threading around VR Scene updates.

chrome/browser/android/vr_shell/ui_scene.cc

Index: chrome/browser/android/vr_shell/ui_scene.cc
diff --git a/chrome/browser/android/vr_shell/ui_scene.cc b/chrome/browser/android/vr_shell/ui_scene.cc
index be4d83b15f0660cc95ea659bc5a7ab779beae070..2d4adb13181229d86665b66925900a5b649193b6 100644
--- a/chrome/browser/android/vr_shell/ui_scene.cc
+++ b/chrome/browser/android/vr_shell/ui_scene.cc
@@ -278,7 +278,7 @@ void UiScene::RemoveAnimation(int element_id, int animation_id) {
   }
 }
 
-void UiScene::HandleCommands(const base::ListValue* commands,
+void UiScene::HandleCommands(std::unique_ptr<base::ListValue> commands,
                              int64_t time_in_micro) {
   for (auto& item : *commands) {
     base::DictionaryValue* dict;
@@ -351,11 +351,6 @@ UiScene::UiScene() = default;
 
 UiScene::~UiScene() = default;
 
-int64_t UiScene::TimeInMicroseconds() {
-  return std::chrono::duration_cast<std::chrono::microseconds>(
-      std::chrono::steady_clock::now().time_since_epoch()).count();
-}
-
 void UiScene::ApplyRecursiveTransforms(const ContentRectangle& element,
                                        ReversibleTransform* transform) {
   transform->Scale(element.scale.x, element.scale.y, element.scale.z);