Mac: Prevent NTP mousewheel events from being suppressed on Lion.

chrome/browser/resources/ntp4/tile_page.js

 // 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.
 
 cr.define('ntp', function() {
   'use strict';
 
   // We can't pass the currently dragging tile via dataTransfer because of
   // http://crbug.com/31037
   var currentlyDraggingTile = null;
@@ skipping 430 matching lines @@
       // These are properties used in updateTopMargin.
       this.animatedTopMarginPx_ = 0;
       this.topMarginPx_ = 0;
 
       this.eventTracker = new EventTracker();
       this.eventTracker.add(window, 'resize', this.onResize_.bind(this));
 
       this.addEventListener('DOMNodeInsertedIntoDocument',
                             this.onNodeInsertedIntoDocument_);
 
-      this.addEventListener('mousewheel', this.onMouseWheel_);

[Patrick Dubroy, 2012/04/17 17:28:24]

We don't need to add a listener to this object, because the event will be
forwarded by the card slider's event handler.

       this.content_.addEventListener('scroll', this.onScroll_.bind(this));
 
       this.dragWrapper_ = new cr.ui.DragWrapper(this.tileGrid_, this);
 
       this.addEventListener('cardselected', this.handleCardSelection_);
       this.addEventListener('carddeselected', this.handleCardDeselection_);
       this.addEventListener('focus', this.handleFocus_);
       this.addEventListener('keydown', this.handleKeyDown_);
       this.addEventListener('mousedown', this.handleMouseDown_);
 
@@ skipping 584 matching lines @@
       * Places an element at the bottom of the content div. Used in bare-minimum
       * mode to hold #footer.
       * @param {HTMLElement} footerNode The node to append to content.
       */
     appendFooter: function(footerNode) {
       this.footerNode_ = footerNode;
       this.content_.appendChild(footerNode);
     },
 
     /**
-     * Scrolls the page in response to a mousewheel event.
+     * Scrolls the page in response to an mousewheel event, although the event
+     * may have been triggered on a different element.
+     * This is called explicitly, which allows a consistent experience whether
+     * the user scrolls on the page or on the page switcher, because this
+     * function provides a common conversion factor between wheel delta and
+     * scroll delta.
      * @param {Event} e The mousewheel event.
      */
     handleMouseWheel: function(e) {
+      if (e.wheelDeltaY == 0)
+        return;
+
       this.content_.scrollTop -= e.wheelDeltaY / 3;
+
+      // Prevent the event from triggering the default scroll behavior on this
+      // element.
+      for (var el = e.target; el; el = el.parentNode) {
+        if (el == this) {
+          e.preventDefault();
+          break;
+        }
+      }
     },
 
     /**
-     * Handles mouse wheels on |this|. We handle this explicitly because we want
-     * a consistent experience whether the user scrolls on the page or on the
-     * page switcher (handleMouseWheel provides a common conversion factor
-     * between wheel delta and scroll delta).
-     * @param {Event} e The mousewheel event.
-     * @private
-     */
-    onMouseWheel_: function(e) {
-      if (e.wheelDeltaY == 0)
-        return;
-
-      this.handleMouseWheel(e);
-      e.preventDefault();
-      e.stopPropagation();
-    },
-
-    /**
      * Handler for the 'scroll' event on |content_|.
      * @param {Event} e The scroll event.
      * @private
      */
     onScroll_: function(e) {
       this.queueUpdateScrollbars_();
     },
 
     /**
      * ID of scrollbar update timer. If 0, there's no scrollbar re-calc queued.
@@ skipping 242 matching lines @@
       assert(false);
     },
   };
 
   return {
     getCurrentlyDraggingTile: getCurrentlyDraggingTile,
     setCurrentDropEffect: setCurrentDropEffect,
     TilePage: TilePage,
   };
 });