Make MIME boundary harder to accidentally match.

This is just making the same change to the copy of upload.py that is in depot_tools.

BUG=419156
R=iannucci@chromium.org

Original Review URL: https://codereview.chromium.org/624513002

Review URL: https://codereview.chromium.org/639503002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@292432 0039d316-1c4b-4281-b951-d872f2087c98

third_party/upload.py

@@ -972,7 +972,7 @@ def EncodeMultipartFormData(fields, files):
   Source:
     http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/146306
   """
-  BOUNDARY = '-M-A-G-I-C---B-O-U-N-D-A-R-Y-'
+  BOUNDARY = '-M-A-G-I-C---B-O-U-N-D-A-R-Y-%s-' % sum(hash(f) for f in files)
   CRLF = '\r\n'
   lines = []
   for (key, value) in fields: