Roll buildtools 10d701fce5..e8aa02ea83

  In order to roll GN ee966518..b709e226 (r544233:r549249) and pick up
  the following changes:

  12bd7ed6 [gn] Updating args --list to make the comment padding optional
  743a7a88 Fix grammar-o in gn's help.
  28f3c498 Implement "friend" for GN header checking.
  f7ccdc76 GN: Use source root as base for gn gen filters
  73b7854e GN: Improve bootstrap for Windows
  8ca5c09b [gn] Updating args --list to emit json
  e65dd61a Fix gn bootstrap
  c89b8fab Fix gn bootstrap

TBR=dpranke@chromium.org

Change-Id: I8dd84acad1d55692938e4980c260145dd50c6e78
Reviewed-on: https://chromium-review.googlesource.com/1003524Reviewed-by: Brett Wilson <brettw@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Brett Wilson <brettw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549393}

DEPS

@@ -98,7 +98,7 @@ 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': '10d701fce52d192005512aa832dc82f9aae72b5d',
+  'buildtools_revision': 'e8aa02ea839e087f2db66100d02c3b5d47993852',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling SwiftShader
   # and whatever else without interference from each other.