Use base namespace for string16 in components and cloud_print.

R=scottbyer@chromium.org
TBR=scottbyer

Review URL: https://codereview.chromium.org/107383002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239255 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239255