Update the VS toolchain hash computation caching.

win_toolchain/get_toolchain_if_necessary.py

 #!/usr/bin/env python
 # Copyright 2013 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.
 
 """Downloads and unpacks a toolchain for building on Windows. The contents are
 matched by sha1 which will be updated when the toolchain is updated.
 
 Having a toolchain script in depot_tools means that it's not versioned
 directly with the source code. That is, if the toolchain is upgraded, but
@@ skipping 147 matching lines @@
   sys.stdout.flush()
   digest = hashlib.sha1()
   for path in file_list:
     path_without_hash = str(path).replace('/', '\\')
     if expected_hash:
       path_without_hash = path_without_hash.replace(
           os.path.join(root, expected_hash).replace('/', '\\'), root)
     digest.update(path_without_hash.lower())
     with open(path, 'rb') as f:
       digest.update(f.read())
+
+  # Save the timestamp file if the calculated hash is the expected one.
+  if digest.hexdigest() == expected_hash:
+    SaveTimestampsAndHash(root, digest.hexdigest())
   return digest.hexdigest()
 
 
 def CalculateToolchainHashes(root, remove_corrupt_toolchains):
   """Calculate the hash of the different toolchains installed in the |root|
   directory."""
   hashes = []
   dir_list = [
       d for d in os.listdir(root) if os.path.isdir(os.path.join(root, d))]
   for d in dir_list:
@@ skipping 358 matching lines @@
   if os.environ.get('GYP_MSVS_VERSION') == '2015':
     InstallUniversalCRTIfNeeded(abs_toolchain_target_dir)
 
   RemoveUnusedToolchains(target_dir)
 
   return 0
 
 
 if __name__ == '__main__':
   sys.exit(main())