Roll buildtools to pull clang-format.

DEPS

 # This file is used to manage the dependencies of the Chromium src repo. It is
 # used by gclient to determine what version of each dependency to check out, and
 # where.
 #
 # For more information, please refer to the official documentation:
 #   https://sites.google.com/a/chromium.org/dev/developers/how-tos/get-the-code
 #
 # When adding a new dependency, please update the top-level .gitignore file
 # to list the dependency's destination directory.
 #
@@ skipping 46 matching lines @@
   # the commit queue can handle CLs rolling swarming_client
   # and whatever else without interference from each other.
   'swarming_revision': 'bcb3bc30328c38441d3f7656cb649b123803726c',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling ANGLE
   # and whatever else without interference from each other.
   "angle_revision": "4de44cb67e9e36966fb1993c0be35659a47182ef",
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling build tools
   # and whatever else without interference from each other.
-  'buildtools_revision': '56bc51aff4175d3fa27dcd0faa2c345ab046c8a5',
+  'buildtools_revision': '51ca1f25a2ecea34069cb3ff35394dc53b6fd657',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling PDFium
   # and whatever else without interference from each other.
   'pdfium_revision': '4dc95e74e1acc75f4eab08bc771874cd2a9c3a9b',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling openmax_dl
   # and whatever else without interference from each other.
   'openmax_dl_revision': '01642706d2b37cb7b9db84add870ea0fdabdf5ad',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling BoringSSL
@@ skipping 696 matching lines @@
     # corresponding .py files have already been deleted.
     'name': 'remove_stale_pyc_files',
     'pattern': 'src/tools/.*\\.py',
     'action': [
         'python',
         'src/tools/remove_stale_pyc_files.py',
         'src/tools',
     ],
   },
 ]