[chrome_remote_control] Add pylint to PRESUMMIT and fix lint

tools/chrome_remote_control/chrome_remote_control/browser_backend.py

 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 import urllib2
 import httplib
 import json
 
 from chrome_remote_control import inspector_backend
 from chrome_remote_control import tab
 from chrome_remote_control import util
@@ skipping 27 matching lines @@
     except util.TimeoutException:
       raise BrowserGoneException()
 
   def _ListTabs(self, timeout=None):
     if timeout:
       req = urllib2.urlopen('http://localhost:%i/json' % self._port,
                             timeout=timeout)
     else:
       req = urllib2.urlopen('http://localhost:%i/json' % self._port)
     data = req.read()
-    return json.loads(data)
+    all_contexts = json.loads(data)
+    tabs = [ctx for ctx in all_contexts
+            if not ctx['url'].startswith('chrome-extension://')]
+    return tabs
 
   @property
   def num_tabs(self):
     return len(self._ListTabs())
 
   def GetNthTabUrl(self, index):
     return self._ListTabs()[index]['url']
 
   def ConnectToNthTab(self, browser, index):
     ib = inspector_backend.InspectorBackend(self, self._ListTabs()[index])
     return tab.Tab(browser, ib)
 
   def CreateForwarder(self, host_port):
     raise NotImplementedError()
 
   def IsBrowserRunning(self):
     raise NotImplementedError()