Adds webkit-patch auto-rebaseline and rebaseline-o-matic.

-auto-rebaseline blames TestExpectations and rebaselines any lines that have
cycled through all the release bots.
-rebaseline-o-matic calls syncs the repo and auto-rebaselines in a loop.
-expose a bunch of git-only scm methods and expose a non-svn blame method
-switch fetch_layout_test_results to looking at failing_results.json.
No need to grab the much larger full_results.json.
-expose executive.call as an alternative to run_command that
doesn't swallow the stdout/stderr.
-change AbstractParallelRebaselineCommand._run_webkit_patch
to use _log instead of directly printing so that the
unittests that indirectly call it don't actually print.

R=dpranke@chromium.org

Review URL: https://codereview.chromium.org/18882003

git-svn-id: svn://svn.chromium.org/blink/trunk@154679 bbb929c8-8fbe-4397-9dbb-9b2b20218538