It does a regexp search on the file contents to make sure it contains expected license boiler plate.

It is a generalization to implement the equivalent of ubuntu's license check script into the corresponding PRESUBMIT.py files.

TEST=unit tests
BUG=28291

Review URL: http://codereview.chromium.org/558007

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@37338 0039d316-1c4b-4281-b951-d872f2087c98