NTP: Register callbacks to prevent race conditions.

This fixes the errors related to bookmarkBarDetached and bookmarkBarAttached.

BUG=69705
TEST=Open NTP.
     Open the error console.
     Reload several times.
     Attach/detach the bookmark bar.
     Reload a few more times
     No errors are shown

Review URL: http://codereview.chromium.org/6359003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@71697 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/resources/new_new_tab.html

@@ -54,6 +54,8 @@ registerCallback('syncMessageChanged');
 registerCallback('getAppsCallback');
 registerCallback('setShownSections');
 registerCallback('foreignSessions');
+registerCallback('bookmarkBarDetached');
+registerCallback('bookmarkBarAttached');
 
 </script>
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