Add blink drover revert support.

Building on crrev.com/12670008, add support for blink svn. The svn
revision for blink is sufficiently different from chromium that we
can revert blink changes without further logic changes. The order of
alternative repos corresponds roughly to the expected rate of use.

TEST=Tried reverting some blink revs.

Review URL: https://chromiumcodereview.appspot.com/13448004

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@192396 0039d316-1c4b-4281-b951-d872f2087c98

drover.py

@@ -490,7 +490,8 @@ def drover(options, args):
   # Initialize some variables used below. They can be overwritten by
   # the drover.properties file.
   BASE_URL = "svn://svn.chromium.org/chrome"
-  REVERT_ALT_URLS = ['svn://svn.chromium.org/chrome-internal',
+  REVERT_ALT_URLS = ['svn://svn.chromium.org/blink',
+                     'svn://svn.chromium.org/chrome-internal',
                      'svn://svn.chromium.org/native_client']
   TRUNK_URL = BASE_URL + "/trunk/src"
   BRANCH_URL = BASE_URL + "/branches/$branch/src"