Allow building with VS 2015 Update 3 pre-release

build/vs_toolchain.py

 #!/usr/bin/env python
 # 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 glob
 import json
 import os
 import pipes
 import shutil
@@ skipping 261 matching lines @@
   runtime_dir = x64_runtime if target_cpu == 'x64' else x86_runtime
   _CopyRuntime(target_dir, runtime_dir, target_cpu, debug=False)
   if configuration == 'Debug':
     _CopyRuntime(target_dir, runtime_dir, target_cpu, debug=True)
 
 
 def _GetDesiredVsToolchainHashes():
   """Load a list of SHA1s corresponding to the toolchains that we want installed
   to build with."""
   if GetVisualStudioVersion() == '2015':
-    # Update 2.
-    return ['95ddda401ec5678f15eeed01d2bee08fcbc5ee97']
+    # Update 3 pre-release, May 9th.
+    return ['97b5c1d5f7c614126da344d55a20dcc424f578eb']

[scottmg, 2016/05/12 18:34:38]

with a

if bool(int(os.environ.get('DEPOT_TOOLS_WIN_TOOLCHAIN_PRERELEASE', '0'))) == 1:

here.

   else:
     return ['03a4e939cd325d6bc5216af41b92d02dda1366a6']
 
 
 def ShouldUpdateToolchain():
   """Check if the toolchain should be upgraded."""
   if not os.path.exists(json_data_file):
     return True
   with open(json_data_file, 'r') as tempf:
     toolchain_data = json.load(tempf)
@@ skipping 75 matching lines @@
       'copy_dlls': CopyDlls,
   }
   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]](*sys.argv[2:])
 
 
 if __name__ == '__main__':
   sys.exit(main())