Update all users of base::Version to explicitly specify the namespace, and clean up the header.

BUG=none
TEST=no change
TBR=ben@chromium.org

Review URL: https://codereview.chromium.org/100543005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242414 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242414