Fix the coverage build which used to complain about the missing pyautolib target.
In the case pyautolib shouldn't be built, define a fake pyautolib target. This lets other targets
to unconditionally depend on pyautolib.

BUG=307018
R=thakis@chromium.org

Review URL: https://codereview.chromium.org/29013002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229837 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 229837