Make gn wrapper use the one in buildtools rather than tools/gn/bin.

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 632 matching lines @@
   """Returns 'mac', 'win', or 'linux', matching the current platform."""
   if sys.platform.startswith(('cygwin', 'win')):
     return 'win'
   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."""
+  gclient_root = FindGclientRoot(os.getcwd())
+  if not gclient_root:
+    return None
+  return os.path.join(gclient_root, 'src', 'buildtools')
+
+
+def GetBuildtoolsPlatformBinaryPath():
+  """Returns the full path to the binary directory for the current platform."""
+  # Mac and Windows just have one directory, Linux has two according to whether
+  # it's 32 or 64 bits.
+  buildtools_path = GetBuildtoolsPath()
+  if not buildtools_path:
+    return None
+
+  if sys.platform.startswith(('cygwin', 'win')):
+    subdir = 'win'
+  elif sys.platform == 'darwin':
+    subdir = 'mac'
+  elif sys.platform.startswith('linux'):
+    if sys.maxsize > 2**32:
+      subdir = 'linux64'
+    else:
+      subdir = 'linux32'
+  else:
+    raise Error('Unknown platform: ' + sys.platform)
+  return os.path.join(buildtools_path, subdir)
+
+
 def GetExeSuffix():
   """Returns '' or '.exe' depending on how executables work on this platform."""
   if sys.platform.startswith(('cygwin', 'win')):
     return '.exe'
   return ''
 
 
 def GetGClientRootAndEntries(path=None):
   """Returns the gclient root and the dict of entries."""
   config_file = '.gclient_entries'
@@ skipping 420 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