Update some uses of char16 to use the base:: namespace.

BUG=329295
TEST=no change
TBR=ben@chromium.org

Review URL: https://codereview.chromium.org/111373008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242507 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242507