Roll buildtools 505de88083..282996b8c3

  In order to roll GN 157d5de4..f3a5b8c1 (r514519:r520777) and pick up
  the following changes:

  7f86d891 gn: Check if formatting a single line list to multiple reduces penalty
  5accd24a Remove base::SizeToToString[16]
  8f449e3d gn: Fix formatting of file containing only 2 block comments
  e643f226 add jumbo support when building gn itself
  e4963ba3 Run clang-tidy modernize-use-equals-{delete,default} on //tools
  5eea716f GN: Fix references to lib_[dir_]prefix, which should be lib_[dir_]switch
  8b6898fe Add option to gn bootstrap to specify the build directory
  3667991e Use std::make_unique in GN code.
  e953738c Clarify GN nonfatal unused build arg messages.
  e03b10a9 Remove unneeded extern keywords in tools/gn.
  976fe5f3 Add observer_list_threadsafe.cc to gn bootstrap deps
  36d1a861 [CFI] Add protected memory container class

TBR=dpranke@chromium.org

Change-Id: I22d358ee205d68100bf6a0d8f0e8129450d89e98
Reviewed-on: https://chromium-review.googlesource.com/802677Reviewed-by: Scott Graham <scottmg@chromium.org>
Commit-Queue: Scott Graham <scottmg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#520841}

DEPS

@@ -90,7 +90,7 @@ 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': '505de88083136eefd056e5ee4ca0f01fe9b33de8',
+  'buildtools_revision': '282996b8c3cf7f05bbb5209432e9fe8162c6e7ac',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling SwiftShader
   # and whatever else without interference from each other.