Use depot_tools toolchain, remove now unneeded code, fix not including path to win sdk tools

build/toolchain/win/BUILD.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/toolchain/goma.gni")
 
 # Should only be running on Windows.
 assert(is_win)
 
 import("//build/config/win/visual_studio_version.gni")
 
 # Setup the Visual Studio state.
 #
 # Its arguments are the VS path and the compiler wrapper tool. It will write
 # "environment.x86" and "environment.x64" to the build directory and return a
 # list to us.
 gyp_win_tool_path = rebase_path("//tools/gyp/pylib/gyp/win_tool.py",
                                 root_build_dir)
-exec_script("setup_toolchain.py", [ visual_studio_path, gyp_win_tool_path ],
+exec_script("setup_toolchain.py",
+            [ visual_studio_path, gyp_win_tool_path, windows_sdk_path ],
             "string")
 
 stamp_command = "$python_path gyp-win-tool stamp \$out"
 copy_command = "$python_path gyp-win-tool recursive-mirror \$in \$out"
 
 if (use_goma) {
   # Add the Goma compiler prefixes to the GYP file.
   gyp_header = "'make_global_settings': [ $make_goma_global_settings ],"
 }
 
@@ skipping 116 matching lines @@
 
   # When invoking this toolchain not as the default one, these args will be
   # passed to the build. They are ignored when this is the default toolchain.
   toolchain_args() {
     cpu_arch = "x64"
     # Normally the build config resets the CPU architecture to 32-bits. Setting
     # this flag overrides that behavior.
     force_win64 = true
   }
 }