Assume 'master' when remote branch not specified.

checkout.py

Index: checkout.py
diff --git a/checkout.py b/checkout.py
index ec308013d42c5163ef617cdcd6d9ff0466615cad..b21f03c7ee3dda776afa82b67a647e71a0899088 100644
--- a/checkout.py
+++ b/checkout.py
@@ -562,6 +562,7 @@ class GitCheckout(CheckoutBase):
     self.git_url = git_url
     self.commit_user = commit_user
     self.remote_branch = remote_branch
+    assert self.remote_branch
     # The working branch where patches will be applied. It will track the
     # remote branch.
     self.working_branch = 'working_branch'
@@ -624,7 +625,9 @@ class GitCheckout(CheckoutBase):
     # trying again?
     if self.remote_branch:

[Ryan Tseng, 2014/03/19 01:54:28]

Maybe "if self.remote_branch and not self.base_ref"?

Since if we have a base_ref set, thats actually the ref we want to base this
patch on top of, rather than the remote branch.

We can't use remote branch because a ref isn't always a branch.

       self._check_call_git(
-          ['checkout', '-b', self.working_branch, '-t', self.remote_branch,
+          ['checkout', 
+           '-b', self.working_branch, 
+           '-t', '%s/%s' % (self.pull_remote, self.remote_branch),

[agable, 2014/03/18 21:19:09]

Ravi: apply_issue was checking out a branch tracking local master rather than
origin/master, which is why the skiabuildbot CQ was failing.

            '--quiet'])
 
     for index, p in enumerate(patches):