[WPT Export] Delete remote branch, add label, additional refactoring

third_party/WebKit/Tools/Scripts/webkitpy/w3c/wpt_github_mock.py

 class MockWPTGitHub(object):
 
     def __init__(self, pull_requests, unsuccessful_merge=False):
         self.pull_requests = pull_requests
         self.unsuccessful_merge = unsuccessful_merge
         self.calls = []
         self.pull_requests_created = []
 
     def in_flight_pull_requests(self):
         self.calls.append('in_flight_pull_requests')
         return self.pull_requests
 
     def merge_pull_request(self, number):
         self.calls.append('merge_pull_request')
         if self.unsuccessful_merge:
             raise Exception('PR could not be merged: %d' % number)
 
-    def create_pr(self, local_branch_name, desc_title, body):
+    def create_pr(self, remote_branch_name, desc_title, body):
         self.calls.append('create_pr')
 
-        assert local_branch_name
+        assert remote_branch_name
         assert desc_title
         assert body
 
-        self.pull_requests_created.append((local_branch_name, desc_title, body))
+        self.pull_requests_created.append((remote_branch_name, desc_title, body))
 
         return {}
+
+    def delete_remote_branch(self, _):
+        self.calls.append('delete_remote_branch')