Roll buildtools 7f2cacbbe2..38477c2e10

  In order to roll GN 7c9bd5f0..bedb4b20 (r465654:r481731) and pick up
  the following changes:

  a104997e Allow overriding script executable in .gn file
  18697c83 Move if, else, true, false into a keyword category
  d4a5e982 [tracing] Switch to new heap dump format.
  8480d866 tools/gn: Implement Windows SDK version command line switch
  3e0d5228 Use ContainsValue() instead of std::find() in tools/
  e4a28698 Fix GN bootstrap
  11857736 [spelling] existance to existence
  21886543 Fix a bug in `gn analyze` for host-only file mods.
  f8bf5083 Fix gn get_label_info comment
  05f56d41 allocator: remove ENABLE_MEMORY_TASK_PROFILER and use only USE_ALLOCATOR_SHIM
  e329e9ec Fix GN bootstrap
  2928b5dc Add information on the requirements for a new Chromium port.
  73228cd4 allocator: rename use_experimental_allocator_shim to use_allocator_shim
  797723cd Fix GN bootstrap
  84fa8b08 Replace sanitizers:deps with exe_and_shlib_deps (Chromium repo only)
  d77555bc GN: Fix single-file compilations in VS2017 projects
  cbbd560a gn: get rid of GetRealPath() function
  cf2a4bf9 gn: convert WrapUnique calls to MakeUnique where possible
  dfb837a9 gn: fix bootstrap on windows
  777e1cd5 Fix gn bootstrap after https://codereview.chromium.org/2872503003
  25e10941 gn: Document gen's --check flag.
  14525201 Add a GUID to base::SharedMemoryHandle.
  b154afcb memory-infra: Move dump level check to observer and rename session state
  9b718c79 Fix GN bootstrap
  643d6bc9 gn: fix bootstrap.py after https://codereview.chromium.org/2846893003
  dd1ae15f gn docs: Add a missing closing paren.
  0088ee50 GN: aix port along with linux_s390x, linux_ppc64 and linux_ppc64le support.
  4a4589fc memory-infra: Start disentangling tracing from memory-infra
  7fd3f671 Add curly brackets to list of characters that gn needs to escape
  ca2ec763 Improvements to uses of base::SmallMap
  ddb3babc Use $root:default as a "default" rule

TBR=brettw@chromium.org

Review-Url: https://codereview.chromium.org/2953643004
Cr-Commit-Position: refs/heads/master@{#481774}

DEPS

@@ -56,7 +56,7 @@ 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': '7f2cacbbe274ef9df2c94452e05e8702c3ae65a9',
+  'buildtools_revision': '38477c2e103caf651d113dad07cd3e4efb992209',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling SwiftShader
   # and whatever else without interference from each other.