ntp4: polish app trashing

chrome/browser/resources/ntp4/tile_page.css

 /* Copyright (c) 2011 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.
  */
 
 .tile-page {
   height: 100%;
   position: relative;
   width: 100%;
 }
@@ skipping 55 matching lines @@
 }
 
 .tile.dragging {
   opacity: 0;
 }
 
 .tile.drag-representation {
   pointer-events: none;
   position: fixed;
   z-index: 3;
+  -webkit-transition: opacity 0.2s;
 }
 
 .tile.drag-representation.placing > * {
   -webkit-transition: -webkit-transform 200ms;
 }
 
 .tile.drag-representation.placing > *.deleting {
   -webkit-transform: scale(0) rotate(360deg);
   -webkit-transition: -webkit-transform 600ms;
 }
 
 .animating-tile-page .tile,
 .tile.drag-representation.placing {
   -webkit-transition: left 200ms, right 200ms, top 200ms;
 }
 
+.hovering-on-trash {
+  opacity: 0.6;
+}
+
 .animating-tile-page .top-margin {
   -webkit-transition: margin-bottom 200ms;
 }
 
 @-webkit-keyframes bounce {
   0% {
     -webkit-transform: scale(0, 0);
   }
 
   60% {
@@ skipping 40 matching lines @@
 
 /** Scrollbars ****************************************************************/
 
 .tile-page-content::-webkit-scrollbar {
   width: 13px;
 }
 
 .tile-page-content::-webkit-scrollbar-button {
   display: none;
 }