ntp: adjust top padding

re-adjusted the padding above the tile grid to have a minimum of 60px rather than 100px, also it scales upwards faster as the page height increases because instead of aligning the middle of the tile grid at 1/3 from the top of the page, we align the 1/3 mark of the tile grid with the 1/3 mark of the page.

the end result is that a browser window <800px tall with 3 rows of apps and a floating bbar still will not have a scrollbar

BUG=101290
TEST=manual


Review URL: http://codereview.chromium.org/8771060

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@113345 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/resources/ntp4/tile_page.css

@@ -23,7 +23,8 @@
 
 .tile-page-content {
   overflow-y: scroll;
-  padding-top: 100px;
+  /* This value is mirrored in TilePage.updateTopMargin_ */
+  padding-top: 60px;
   position: relative;
   text-align: center;
   width: 100%;

chrome/browser/resources/ntp4/tile_page.js

@@ -897,9 +897,9 @@ cr.define('ntp4', function() {
           (this.isCurrentDragTarget && !this.withinPageDrag_ ? 1 : 0);
       var numRows = Math.ceil(numTiles / layout.numRowTiles);
       var usedHeight = layout.rowHeight * numRows;
-      // 100 matches the top padding of tile-page.
+      // 60 matches the top padding of tile-page (which acts as the minimum).
       var newMargin = document.documentElement.clientHeight / 3 -
-          usedHeight / 2 - 100 - this.content_.offsetTop;
+          usedHeight / 3 - 60;
       newMargin = Math.max(newMargin, 0);
 
       // |newMargin| is the final margin we actually want to show. However,