1. GetFileList() returns a list of path\names on Windows but of path/names on
   non-Windows. To not perturb existing hashes, I guess the hashing code should do
   path.replace('/', '\\') before hashing.

2. GetFileList() returns a sorted list of filenames, and \ compares pretty
   different than / (the former is less than all numbers while the latter
   is greater, for example).  So replace / with \\ for sorting too.

With this change, OS X produces the same file hash as Windows.

The script still early-exits on non-Windows, so no visible change yet.

BUG=495204

Review URL: https://codereview.chromium.org/1287543005

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@296271 0039d316-1c4b-4281-b951-d872f2087c98