Consolidated 'git' refish parsing into a class

Created the 'GitRefish' class to centralize 'git' refish parsing and consistent
usage by 'gclient' 'git' code.

BUG=373504
TEST=localtest
R=agable@chromium.org, iannucci@chromium.org

Review URL: https://codereview.chromium.org/328843005

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@281553 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/gclient.py b/gclient.py
index a2d159a..275dad3 100755
--- a/gclient.py
+++ b/gclient.py
@@ -1112,7 +1112,7 @@
       if dep.managed and dep.url:
         scm = gclient_scm.CreateSCM(
             dep.url, self.root_dir, dep.name, self.outbuf)
-        actual_url = scm.GetActualRemoteURL(self._options)
+        actual_url = scm.GetActualRemoteURL()
         if actual_url and not scm.DoesRemoteURLMatch(self._options):
           raise gclient_utils.Error('''
 Your .gclient file seems to be broken. The requested URL is different from what