Allow themes to change the background of the new tab page....

chrome/browser/resources/new_tab_theme.css

Index: chrome/browser/resources/new_tab_theme.css
===================================================================
--- chrome/browser/resources/new_tab_theme.css	(revision 17403)
+++ chrome/browser/resources/new_tab_theme.css	(working copy)
@@ -1,11 +1,21 @@
-body {
+html {
   background-image:url(chrome://theme/theme_ntp_background?$1);
-  background-position:bottom;
-  color: $2;
+  background-color:$2;
+  background-position:$3;
+  background-repeat:no-repeat;
+  overflow:hidden;
 }
+html[bookmarkbarattached='true'] {
+  background-position:$4;
+}
+body {
+  color: $5;
+  height:100%;
+  overflow:auto;
+}
 a {
-  color: $3;
+  color: $6;
 }
 .sidebar.themed {
-  background-color: $4;
+  background-color: $7;
 }