Revert of Roll buildtools 7f2cacbbe2..38477c2e10 (patchset #1 id:1 of...

Revert of Roll buildtools 7f2cacbbe2..38477c2e10 (patchset #1 id:1 of https://codereview.chromium.org/2953643004/ )

Reason for revert:
Probably broke incremental builds on trybots.

BUG=736215

Original issue's description:
> 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}
> Committed: https://chromium.googlesource.com/chromium/src/+/3391d2ce4059ebe801dd8310d13d8dc59293600e

TBR=brettw@chromium.org,dpranke@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review-Url: https://codereview.chromium.org/2956623002
Cr-Commit-Position: refs/heads/master@{#481839}

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