Update from https://crrev.com/303153

build/vs_toolchain.py

 # Copyright 2014 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.
 
 import json
 import os
 import pipes
 import shutil
 import subprocess
 import sys
 
 
 script_dir = os.path.dirname(os.path.realpath(__file__))
 chrome_src = os.path.abspath(os.path.join(script_dir, os.pardir))
 SRC_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
 sys.path.insert(1, os.path.join(chrome_src, 'tools'))
 sys.path.insert(0, os.path.join(chrome_src, 'tools', 'gyp', 'pylib'))
 json_data_file = os.path.join(script_dir, 'win_toolchain.json')
 
 
+import gyp
+
+
 def SetEnvironmentAndGetRuntimeDllDirs():
   """Sets up os.environ to use the depot_tools VS toolchain with gyp, and
   returns the location of the VS runtime DLLs so they can be copied into
   the output directory after gyp generation.
   """
   vs2013_runtime_dll_dirs = None
   depot_tools_win_toolchain = \
       bool(int(os.environ.get('DEPOT_TOOLS_WIN_TOOLCHAIN', '1')))
   if sys.platform in ('win32', 'cygwin') and depot_tools_win_toolchain:
     if not os.path.exists(json_data_file):
       Update()
     with open(json_data_file, 'r') as tempf:
       toolchain_data = json.load(tempf)
 
     toolchain = toolchain_data['path']
     version = toolchain_data['version']
     version_is_pro = version[-1] != 'e'
     win8sdk = toolchain_data['win8sdk']
     wdk = toolchain_data['wdk']
     # TODO(scottmg): The order unfortunately matters in these. They should be
     # split into separate keys for x86 and x64. (See CopyVsRuntimeDlls call
     # below). http://crbug.com/345992
     vs2013_runtime_dll_dirs = toolchain_data['runtime_dirs']
 
     os.environ['GYP_MSVS_OVERRIDE_PATH'] = toolchain
     os.environ['GYP_MSVS_VERSION'] = version
+    # We need to make sure windows_sdk_path is set to the automated
+    # toolchain values in GYP_DEFINES, but don't want to override any
+    # otheroptions.express
+    # values there.
+    gyp_defines_dict = gyp.NameValueListToDict(gyp.ShlexEnv('GYP_DEFINES'))
+    gyp_defines_dict['windows_sdk_path'] = win8sdk
+    os.environ['GYP_DEFINES'] = ' '.join('%s=%s' % (k, pipes.quote(str(v)))
+        for k, v in gyp_defines_dict.iteritems())
     os.environ['WINDOWSSDKDIR'] = win8sdk
     os.environ['WDK_DIR'] = wdk
     # Include the VS runtime in the PATH in case it's not machine-installed.
     runtime_path = ';'.join(vs2013_runtime_dll_dirs)
     os.environ['PATH'] = runtime_path + ';' + os.environ['PATH']
   return vs2013_runtime_dll_dirs
 
 
 def CopyVsRuntimeDlls(output_dir, runtime_dirs):
   """Copies the VS runtime DLLs from the given |runtime_dirs| to the output
@@ skipping 124 matching lines @@
       # CopyVsRuntimeDlls via import, currently).
   }
   if len(sys.argv) < 2 or sys.argv[1] not in commands:
     print >>sys.stderr, 'Expected one of: %s' % ', '.join(commands)
     return 1
   return commands[sys.argv[1]]()
 
 
 if __name__ == '__main__':
   sys.exit(main())