Roll buildtools from 93b32d0 -> d4dd4f79 to get a new GN build.

This picks up:

    Roll the GN binaries to #318791.

    Roll the GN binaries from 317120:318791 (from git 74add9fc
    to 3d7a60db).

    This fixes 'gn clean' and picks up some new features for
    introspections (see #317159).

TBR=brettw@chromium.org
BUG=430215

Review URL: https://codereview.chromium.org/965963002

Cr-Commit-Position: refs/heads/master@{#318952}

DEPS

@@ -62,8 +62,7 @@ vars = {
   # 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': '93b3d0af1b30db55ee42bd2e983f7753153217db',
+  'buildtools_revision': 'd4dd4f79f60bf019625b3a1436979b0a42c892df',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling PDFium
   # and whatever else without interference from each other.