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: https://src.chromium.org/chrome/trunk/src/url@242507 4ff67af0-8c30-449e-8e8b-ad334ec8d88c