Fix infinite recursion in find_depot_tools

tools/find_depot_tools.py

 # Copyright (c) 2011 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.
 """Small utility function to find depot_tools and add it to the python path.
 
 Will throw an ImportError exception if depot_tools can't be found since it
 imports breakpad.
 """
 
 import os
 import sys
 
 def add_depot_tools_to_path():
   """Search for depot_tools and add it to sys.path."""
   # First look if depot_tools is already in PYTHONPATH.
   for i in sys.path:
     if i.rstrip(os.sep).endswith('depot_tools'):
       return i
   # Then look if depot_tools is in PATH, common case.
   for i in os.environ['PATH'].split(os.pathsep):
     if i.rstrip(os.sep).endswith('depot_tools'):
       sys.path.append(i.rstrip(os.sep))
       return i
   # Rare case, it's not even in PATH, look upward up to root.
   root_dir = os.path.dirname(os.path.abspath(__file__))
-  while root_dir:
+  previous_dir = os.path.abspath(__file__)
+  while root_dir and root_dir != previous_dir:
     if os.path.isfile(os.path.join(root_dir, 'depot_tools', 'breakpad.py')):
       i = os.path.join(root_dir, 'depot_tools')
       sys.path.append(i)
       return i
+    previous_dir = root_dir
     root_dir = os.path.dirname(root_dir)
   print >> sys.stderr, 'Failed to find depot_tools'
   return None
 
 add_depot_tools_to_path()
 
 # pylint: disable=W0611
 import breakpad