Allow chromium buildtools path to be overriden in the environment.

gclient_utils.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.
 
 """Generic utils."""
 
 import codecs
 import cStringIO
 import datetime
 import logging
@@ skipping 640 matching lines @@
   elif sys.platform.startswith('linux'):
     return 'linux'
   elif sys.platform == 'darwin':
     return 'mac'
   raise Error('Unknown platform: ' + sys.platform)
 
 
 def GetBuildtoolsPath():
   """Returns the full path to the buildtools directory.
   This is based on the root of the checkout containing the current directory."""
+
+  # Overriding the build tools path by environment is highly unsupported and may
+  # break without warning.  Do not rely on this for anything important.
+  override = os.environ.get('CHROMIUM_BUILDTOOLS_PATH')
+  if override is not None:
+    return override
+
   gclient_root = FindGclientRoot(os.getcwd())
   if not gclient_root:
     # Some projects might not use .gclient. Try to see whether we're in a git
     # checkout.
     top_dir = [os.getcwd()]
     def filter_fn(line):
       top_dir[0] = os.path.normpath(line.rstrip('\n'))
     try:
       CheckCallAndFilter(["git", "rev-parse", "--show-toplevel"],
                          print_stdout=False, filter_fn=filter_fn)
@@ skipping 463 matching lines @@
 def DefaultIndexPackConfig(url=''):
   """Return reasonable default values for configuring git-index-pack.
 
   Experiments suggest that higher values for pack.threads don't improve
   performance."""
   cache_limit = DefaultDeltaBaseCacheLimit()
   result = ['-c', 'core.deltaBaseCacheLimit=%s' % cache_limit]
   if url in THREADED_INDEX_PACK_BLACKLIST:
     result.extend(['-c', 'pack.threads=1'])
   return result