Remove ICU header dependencies outside of /i18n directory.

      Committing for tsepez. Original code review is here http://codereview.chromium.org/5682002/

BUG=49747
TEST=WordIteratorTest.*
Review URL: http://codereview.chromium.org/5718003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@68867 0039d316-1c4b-4281-b951-d872f2087c98