Revert 232657 "GN: toolchain threading cleanup"

trunk/src/tools/gn/test_with_scope.cc

 // 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.
 
 #include "tools/gn/test_with_scope.h"
 
 TestWithScope::TestWithScope()
     : build_settings_(),
-      settings_(&build_settings_, std::string()),
-      toolchain_(&settings_, Label(SourceDir("//toolchain/"), "default")),
+      toolchain_(Label(SourceDir("//toolchain/"), "tc")),
+      settings_(&build_settings_, &toolchain_, std::string()),
       scope_(&settings_) {
-  build_settings_.SetBuildDir(SourceDir("//out/Debug/"));
-
-  settings_.set_toolchain_label(toolchain_.label());
-  settings_.set_is_default(true);
 }
 
 TestWithScope::~TestWithScope() {
 }