Fix gclient to correctly check out remote refs during update.

Currently, any bot run with "--revision=project@origin/master" fails, because
it fetches the remote ref into refs/remotes/origin/master, but then checks out
refs/heads/master, which hasn't been rolled forward. This is very similar to
the bug fixed by https://codereview.chromium.org/85473007

However, I am very wary of this patch, because I am worried about changing
something commented with " For compatibility...". Marc-Antoine, please comment.

R=maruel@chromium.org, smut@chromium.org, stip@chromium.org

Review URL: https://codereview.chromium.org/244253007

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@266251 0039d316-1c4b-4281-b951-d872f2087c98

gclient_scm.py

@@ -342,8 +342,8 @@ class GitWrapper(SCMWrapper):
     if revision.startswith('refs/'):
       rev_type = "branch"
     elif revision.startswith(self.remote + '/'):
-      # For compatibility with old naming, translate 'origin' to 'refs/heads'
-      revision = revision.replace(self.remote + '/', 'refs/heads/')
+      # Rewrite remote refs to their local equivalents.
+      revision = 'refs/remotes/' + revision
       rev_type = "branch"
     else:
       # hash is also a tag, only make a distinction at checkout