This will have the revision set properly to 'HEAD' before attempting
to apply the patch.
It should also solve the problem that analyze is ending up with
no changes when running 'git diff'.

Expectation update in: https://codereview.chromium.org/1984673002

BUG=438952

Review-Url: https://codereview.chromium.org/1977373002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@300603 0039d316-1c4b-4281-b951-d872f2087c98