ntp4: fix some bugs that appeared when I changed the margin size

chrome/browser/resources/ntp4/tile_page.js

 // 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.
 
 cr.define('ntp4', function() {
   'use strict';
 
   // We can't pass the currently dragging tile via dataTransfer because of
   // http://crbug.com/31037
   var currentlyDraggingTile = null;
@@ skipping 373 matching lines @@
 
       // Div that sets the vertical position of the tile grid.
       this.topMargin_ = this.ownerDocument.createElement('div');
       this.topMargin_.className = 'top-margin';
       this.content_.appendChild(this.topMargin_);
 
       // Div that holds the tiles.
       this.tileGrid_ = this.ownerDocument.createElement('div');
       this.tileGrid_.className = 'tile-grid';
       this.tileGrid_.style.minWidth = (this.gridValues_.minColCount *
-          this.gridValues_.minTileWidth) + 'px';
+          tileWidthFraction(this.gridValues_.minTileWidth)) + 'px';
       this.content_.appendChild(this.tileGrid_);
 
       // Ordered list of our tiles.
       this.tileElements_ = this.tileGrid_.getElementsByClassName('tile real');
 
       // These are properties used in updateTopMargin.
       this.animatedTopMarginPx_ = 0;
       this.topMarginPx_ = 0;
 
       this.eventTracker = new EventTracker();
@@ skipping 200 matching lines @@
         this.tileGrid_.style.height = (realY + layout.rowHeight) + 'px';
         this.queueUpdateScrollbars_();
       }
     },
 
     /**
      * Gets the index of the tile that should occupy coordinate (x, y). Note
      * that this function doesn't care where the tiles actually are, and will
      * return an index even for the space between two tiles. This function is
      * effectively the inverse of |positionTile_|.
-     * @param {number} x The x coordinate, in pixels, relative to the top left
-     *     of tileGrid_.
-     * @param {number} y The y coordinate.
+     * @param {number} x The x coordinate, in pixels, relative to the left of
+     *     |this|.
+     * @param {number} y The y coordinate, in pixels, relative to the top of
+     *     |this|.
      * @private
      */
     getWouldBeIndexForPoint_: function(x, y) {
       var grid = this.gridValues_;
       var layout = this.layoutValues_;
 
-      var col = Math.floor((x - layout.leftMargin) / layout.colWidth);
+      var gridClientRect = this.tileGrid_.getBoundingClientRect();
+      var col = Math.floor((x - gridClientRect.left - layout.leftMargin) /
+                           layout.colWidth);
       if (col < 0 || col >= layout.numRowTiles)
         return -1;
 
       if (ntp4.isRTL())
         col = layout.numRowTiles - 1 - col;
 
-      var row = Math.floor(
-          (y - this.tileGrid_.getBoundingClientRect().top) / layout.rowHeight);
+      var row = Math.floor((y - gridClientRect.top) / layout.rowHeight);
       return row * layout.numRowTiles + col;
     },
 
     /**
      * Window resize event handler. Window resizes may trigger re-layouts.
      * @param {Object} e The resize event.
      */
     onResize_: function(e) {
       if (this.lastWidth_ == this.clientWidth &&
           this.lastHeight_ == this.clientHeight) {
@@ skipping 352 matching lines @@
      */
     tileMoved: function(draggedTile) {
     },
   };
 
   return {
     getCurrentlyDraggingTile: getCurrentlyDraggingTile,
     TilePage: TilePage,
   };
 });