Move more uses of string16 to specify base::

This makes base, ui, and net compile without the "using base::string16" directive that's currently checked in.

BUG=

Review URL: https://codereview.chromium.org/100303003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238246 0039d316-1c4b-4281-b951-d872f2087c98
41 files changed