Reland of "Apply Shelf/Dock opacity animations for the Material Design style."

ash/shelf/shelf_view.cc

 // Copyright (c) 2012 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.
 
 #include "ash/shelf/shelf_view.h"
 
 #include <algorithm>
 #include <memory>
 
 #include "ash/aura/wm_window_aura.h"
@@ skipping 787 matching lines @@
     AnimateToIdealBounds();
     return;
   }
 
   IdealBounds ideal_bounds;
   CalculateIdealBounds(&ideal_bounds);
   views::ViewModelUtils::SetViewBoundsToIdealBounds(*view_model_);
   overflow_button_->SetBoundsRect(ideal_bounds.overflow_bounds);
 }
 
+void ShelfView::UpdateShelfItemBackground(int alpha) {
+  GetAppListButton()->SetBackgroundAlpha(alpha);
+  overflow_button_->SetBackgroundAlpha(alpha);
+}
+
 void ShelfView::UpdateAllButtonsVisibilityInOverflowMode() {
   // The overflow button is not shown in overflow mode.
   overflow_button_->SetVisible(false);
   DCHECK_LT(last_visible_index_, view_model_->view_size());
   for (int i = 0; i < view_model_->view_size(); ++i) {
     bool visible = i >= first_visible_index_ && i <= last_visible_index_;
     // To track the dragging of |drag_view_| continuously, its visibility
     // should be always true regardless of its position.
     if (dragged_off_from_overflow_to_shelf_ &&
         view_model_->view_at(i) == drag_view_)
@@ skipping 1090 matching lines @@
 
 int ShelfView::CalculateShelfDistance(const gfx::Point& coordinate) const {
   const gfx::Rect bounds = GetBoundsInScreen();
   int distance = shelf_->SelectValueForShelfAlignment(
       bounds.y() - coordinate.y(), coordinate.x() - bounds.right(),
       bounds.x() - coordinate.x());
   return distance > 0 ? distance : 0;
 }
 
 }  // namespace ash