[cr tool] Adding the main function and remaining pieces.

tools/cr/cr/autocomplete.py

Index: tools/cr/cr/autocomplete.py
diff --git a/tools/cr/cr/autocomplete.py b/tools/cr/cr/autocomplete.py
new file mode 100644
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+++ b/tools/cr/cr/autocomplete.py
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+# Copyright (c) 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.
+
+"""Bash auto completion support.
+
+Contains the special mode that returns lists of possible completions for the
+current command line.
+"""
+
+import cr
+
+
+def Complete(context):
+  """Attempts to build a completion list for the current command line.
+
+  COMP_WORD contains the word that is being completed, and COMP_CWORD has
+  the index of that word on the command line.
+
+  Args:
+    context: The cr context object, of type cr.context.Context.
+  """
+
+  _ = context
+  # TODO(iancottrell): support auto complete of more than just the command
+  # try to parse the command line using parser
+  print ' '.join(command.name for command in cr.Command.Plugins())