Don't highlight branches named 'origin-foo'

Logic for highlighting "origin/master" (etc) just looked for "origin"
as a prefix. Add the slash since "origin-foo" is a boring old valid
topic branch name.

R=iannucci@chromium.org, iannucci@google.com

Review URL: https://codereview.chromium.org/1832973002 .

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@299486 0039d316-1c4b-4281-b951-d872f2087c98

git_map_branches.py

@@ -174,7 +174,7 @@ class BranchMapper(object):
     return not parent or parent in self.__gone_branches
 
   def __color_for_branch(self, branch, branch_hash):
-    if branch.startswith('origin'):
+    if branch.startswith('origin/'):
       color = Fore.RED
     elif branch.startswith('branch-heads'):
       color = Fore.BLUE