ntp4: polish app trashing

- don't allow un-uninstallable apps to be trashed
- fade effect when dragging over trash

BUG=90894
TEST=manual

Review URL: http://codereview.chromium.org/7572041

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@95640 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/resources/ntp4/tile_page.css

@@ -73,6 +73,7 @@
   pointer-events: none;
   position: fixed;
   z-index: 3;
+  -webkit-transition: opacity 0.2s;
 }
 
 .tile.drag-representation.placing > * {
@@ -89,6 +90,10 @@
   -webkit-transition: left 200ms, right 200ms, top 200ms;
 }
 
+.hovering-on-trash {
+  opacity: 0.6;
+}
+
 .animating-tile-page .top-margin {
   -webkit-transition: margin-bottom 200ms;
 }

chrome/browser/resources/ntp4/trash.js

@@ -29,7 +29,15 @@ cr.define('ntp4', function() {
      * @return {bool}
      */
     shouldAcceptDrag: function(e) {
-      return !!ntp4.getCurrentlyDraggingTile().querySelector('.app');
+      var tile = ntp4.getCurrentlyDraggingTile();
+      if (!tile)
+        return false;
+
+      var app = tile.querySelector('.app');
+      if (!app)
+        return false;
+
+      return app.appData.can_uninstall;
     },
 
     /**
@@ -37,6 +45,8 @@ cr.define('ntp4', function() {
      * @param {Event} e The drag event.
      */
     doDragOver: function(e) {
+      ntp4.getCurrentlyDraggingTile().dragClone.classList.add(
+          'hovering-on-trash');
       e.preventDefault();
       e.dataTransfer.dropEffect = 'move';
     },
@@ -73,6 +83,8 @@ cr.define('ntp4', function() {
      * @param {Event} e The drag event.
      */
     doDragLeave: function(e) {
+      ntp4.getCurrentlyDraggingTile().dragClone.classList.remove(
+          'hovering-on-trash');
     },
   };