Fix bugs with baseline optimizing virtual test suites.

Some of the code is not covered by unittests since we mock out
_move_baselines. These were some places where we were double
including the virtual/foo directory. _join_directory, does
the right thing now.

Review URL: https://chromiumcodereview.appspot.com/21084008

git-svn-id: svn://svn.chromium.org/blink/trunk@155186 bbb929c8-8fbe-4397-9dbb-9b2b20218538