Add a warning when RunUnitTestsInDirectory() finds no test to run to
catch this kind of regression.

Fix all the regressions that where introduced in the meantime...

TBR=dpranke@chromium.org
BUG=
TEST=


Review URL: http://codereview.chromium.org/7906009

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@101347 0039d316-1c4b-4281-b951-d872f2087c98