Ensure most visited pages are up-to-date when showing NTP.

BUG=302433

Review URL: https://codereview.chromium.org/25890003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226955 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226955