[gn] Hard-code msvs version 2013 in MB.

tools/mb/mb.py

 #!/usr/bin/env python
 # Copyright 2016 the V8 project authors. All rights reserved.
 # Copyright 2015 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.
 
 """MB - the Meta-Build wrapper around GYP and GN
 
 MB is a wrapper script for GYP and GN that can be used to generate build files
 for sets of canned configurations and analyze them.
@@ skipping 18 matching lines @@
 
 from collections import OrderedDict
 
 CHROMIUM_SRC_DIR = os.path.dirname(os.path.dirname(os.path.dirname(
     os.path.abspath(__file__))))
 sys.path = [os.path.join(CHROMIUM_SRC_DIR, 'build')] + sys.path
 
 import gn_helpers
 
 
+# We override this here as some legacy gyp scripts are still called through gn.
+# They rely on the environment variable or otherwise use chromium's default of
+# 2015.
+# TODO(machenbach): For switching to msvs 2015, simply remove this.
+MSVS_VERSION = '2013'
+
+
 def main(args):
   mbw = MetaBuildWrapper()
   return mbw.Main(args)
 
 
 class MetaBuildWrapper(object):
   def __init__(self):
     self.chromium_src_dir = CHROMIUM_SRC_DIR
     self.default_config = os.path.join(self.chromium_src_dir, 'infra', 'mb',
                                        'mb_config.pyl')
@@ skipping 721 matching lines @@
           gn_labels.append(gn_isolate_map[target_name]['label'])
 
       if err:
           raise MBErr('Error: Failed to match swarming targets to %s:\n%s' %
                       ('//testing/buildbot/gn_isolate_map.pyl', err))
 
       gn_runtime_deps_path = self.ToAbsPath(build_dir, 'runtime_deps')
       self.WriteFile(gn_runtime_deps_path, '\n'.join(gn_labels) + '\n')
       cmd.append('--runtime-deps-list-file=%s' % gn_runtime_deps_path)
 
-    ret, _, _ = self.Run(cmd)
+    # Override msvs infra environment variables.
+    env = {}
+    env.update(os.environ)
+    env['GYP_MSVS_VERSION'] = MSVS_VERSION
+
+    ret, _, _ = self.Run(cmd, env=env)
     if ret:
         # If `gn gen` failed, we should exit early rather than trying to
         # generate isolates. Run() will have already logged any error output.
         self.Print('GN gen failed: %d' % ret)
         return ret
 
     android = 'target_os="android"' in vals['gn_args']
     for target in swarming_targets:
       if android:
         # Android targets may be either android_apk or executable. The former
@@ skipping 700 matching lines @@
   # Then check to see if the arg contains any metacharacters other than
   # double quotes; if it does, quote everything (including the double
   # quotes) for safety.
   if any(a in UNSAFE_FOR_CMD for a in arg):
     arg = ''.join('^' + a if a in ALL_META_CHARS else a for a in arg)
   return arg
 
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv[1:]))