Rename Mojo targets to have a mojo_ prefix.

To avoid polluting the global target namespace, we should make sure all
the Mojo targets have a mojo_ prefix.

BUG=324635
TEST=mojob.sh test
R=abarth@chromium.org

Review URL: https://codereview.chromium.org/110713003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239995 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239995