Update from https://crrev.com/303153

build/vs_toolchain.py

Index: build/vs_toolchain.py
diff --git a/build/vs_toolchain.py b/build/vs_toolchain.py
index 4ef3a1e8e2ebebd843fb18e300de979405e9ad3c..bdedd6fa8822f121da2687d338cbdf3f58140575 100644
--- a/build/vs_toolchain.py
+++ b/build/vs_toolchain.py
@@ -18,6 +18,9 @@ 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
@@ -44,6 +47,14 @@ def SetEnvironmentAndGetRuntimeDllDirs():
 
     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.