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 70 matching lines @@
   # ignored_directories list isn't relevant on non-Windows hosts.
 
   ignored_directories = ['wer\\reportqueue',
                          'win_sdk\\debuggers\\x86\\sym\\',
                          'win_sdk\\debuggers\\x64\\sym\\']
   for base, _, files in os.walk(root):
     paths = [os.path.join(base, f) for f in files]
     for p in paths:
       if any(ignored_dir in p.lower() for ignored_dir in ignored_directories):
         continue
-      file_list.append(p)
+      file_list.append(p.lower())

[hans, 2016/06/08 17:07:55]

This would essentially undo https://codereview.chromium.org/2039563002/

The point of that patch was to keep the correct case in the list from
GetFileList(), because otherwise many files (e.g. DIA SDK/) won't be found on
case-sensitive filesystems.

Maybe what we want to do is make the comparison on line 130 case-insensitive.

Or, maybe better, if we do the full hash computation on line 156, call
SaveTimestampsAndHash to cache it. Currently it seems the cache is only written
after downloading a new toolchain.

   return sorted(file_list, key=lambda s: s.replace('/', '\\').lower())
 
 
 def MakeTimestampsFileName(root, sha1):
   return os.path.join(root, os.pardir, '%s.timestamps' % sha1)
 
 
 def CalculateHash(root, expected_hash):
   """Calculates the sha1 of the paths to all files in the given |root| and the
   contents of those files, and returns as a hex string.
@@ skipping 434 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())