Replaced BackgroundAnimator with ShelfBackgroundAnimator.

ash/system/tray/tray_background_view.cc

Index: ash/system/tray/tray_background_view.cc
diff --git a/ash/system/tray/tray_background_view.cc b/ash/system/tray/tray_background_view.cc
index 28a3764ba5d703467f2f117c0e850de95759b69d..84bb44a9d6bc2a8a1c93ff1a54176a151503a370 100644
--- a/ash/system/tray/tray_background_view.cc
+++ b/ash/system/tray/tray_background_view.cc
@@ -97,29 +97,24 @@ class TrayBackground : public views::Background {
   const static int kImageVertical = 1;
   const static int kNumOrientations = 2;
 
-  explicit TrayBackground(TrayBackgroundView* tray_background_view) :
-      tray_background_view_(tray_background_view) {
-  }
+  explicit TrayBackground(TrayBackgroundView* tray_background_view)
+      : tray_background_view_(tray_background_view), alpha_(0) {}
 
   ~TrayBackground() override {}
 
+  void set_alpha(int alpha) { alpha_ = alpha; }
+
  private:
   ShelfWidget* GetShelfWidget() const {
     return tray_background_view_->GetShelfLayoutManager()->shelf_widget();
   }
 
   void PaintMaterial(gfx::Canvas* canvas, views::View* view) const {
-    SkColor color = SK_ColorTRANSPARENT;
-    ShelfWidget* shelf_widget = GetShelfWidget();
+    SkColor color = SkColorSetA(kShelfBaseColor, alpha_);
     if (tray_background_view_->draw_background_as_active()) {
       // TODO(bruthig|mohsen): Use of this color is temporary. Draw the active
       // state using the material design ripple animation.
       color = SK_ColorBLUE;
-    } else if (shelf_widget &&
-               shelf_widget->GetBackgroundType() ==
-                   ShelfBackgroundType::SHELF_BACKGROUND_DEFAULT) {
-      color = SkColorSetA(kShelfBaseColor,
-                          GetShelfConstant(SHELF_BACKGROUND_ALPHA));
     }
 
     // TODO(bruthig|tdanderson): The background should be changed using a
@@ -176,6 +171,8 @@ class TrayBackground : public views::Background {
   // Reference to the TrayBackgroundView for which this is a background.
   TrayBackgroundView* tray_background_view_;
 
+  int alpha_;
+
   DISALLOW_COPY_AND_ASSIGN(TrayBackground);
 };
 
@@ -378,13 +375,6 @@ void TrayBackgroundView::OnGestureEvent(ui::GestureEvent* event) {
   ActionableView::OnGestureEvent(event);
 }
 
-void TrayBackgroundView::UpdateBackground(int alpha) {
-  // The animator should never fire when the alternate shelf layout is used.

[James Cook, 2016/06/14 17:50:02]

Hooray for eliminating old "alternate shelf layout" code!

-  if (!background_ || draw_background_as_active_)
-    return;
-  SchedulePaint();
-}
-
 void TrayBackgroundView::SetContents(views::View* contents) {
   SetLayoutManager(new views::BoxLayout(views::BoxLayout::kVertical, 0, 0, 0));
   AddChildView(contents);
@@ -573,4 +563,10 @@ void TrayBackgroundView::UpdateBubbleViewArrow(
   // Nothing to do here.
 }
 
+void TrayBackgroundView::UpdateShelfItemBackground(int alpha) {
+  if (background_)
+    background_->set_alpha(alpha);
+  SchedulePaint();
+}
+
 }  // namespace ash