[cr tool] Make context implicit

tools/cr/cr/commands/shell.py

 # Copyright 2013 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.
 
 """A module for the shell command."""
 
 import os
 import tempfile
 
 import cr
@@ skipping 17 matching lines @@
         in that shell.
         This allows you to run commands that are not yet available natively
         in cr.
         """)
 
   def AddArguments(self, subparsers):
     parser = super(ShellCommand, self).AddArguments(subparsers)
     self.ConsumeArgs(parser, 'the shell')
     return parser
 
-  def Run(self, context):
-    if context.remains:
-      cr.Host.Shell(context, *context.remains)
+  def Run(self):
+    if cr.context.remains:
+      cr.Host.Shell(*cr.context.remains)
       return
     # If we get here, we are trying to launch an interactive shell
     shell = os.environ.get('SHELL', None)
     if shell is None:
       print 'Don\'t know how to run a shell on this system'
     elif shell.endswith('bash'):
       ps1 = '[CR] ' + os.environ.get('PS1', '')
       with tempfile.NamedTemporaryFile() as rcfile:
         rcfile.write('source ~/.bashrc\nPS1="'+ps1+'"')
         rcfile.flush()
-        cr.Host.Execute(context, shell, '--rcfile', rcfile.name)
+        cr.Host.Execute(shell, '--rcfile', rcfile.name)
     else:
-      cr.Host.Execute(context, shell)
+      cr.Host.Execute(shell)