Add initial prototype for the GN meta-buildsystem.

tools/gn/settings.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/settings.h"
+
+#include "base/logging.h"
+#include "tools/gn/filesystem_utils.h"
+
+Settings::Settings(const BuildSettings* build_settings,
+                   const Toolchain* toolchain,
+                   const std::string& output_subdir_name)
+    : build_settings_(build_settings),
+      toolchain_(toolchain),
+      target_os_(WIN),  // FIXME(brettw) set this properly.
+      import_manager_(),
+      base_config_(this) {
+  DCHECK(output_subdir_name.find('/') == std::string::npos);
+  if (output_subdir_name.empty()) {
+    toolchain_output_dir_ = build_settings->build_dir();
+  } else {
+    // We guarantee this ends in a slash.
+    toolchain_output_subdir_.value().append(output_subdir_name);
+    toolchain_output_subdir_.value().push_back('/');
+
+    toolchain_output_dir_ = SourceDir(build_settings->build_dir().value() +
+                                      toolchain_output_subdir_.value());
+  }
+  // The output dir will be null in some tests and when invoked to parsed
+  // one-off data without doing generation.
+  if (!toolchain_output_dir_.is_null())
+    toolchain_gen_dir_ = SourceDir(toolchain_output_dir_.value() + "gen/");
+}
+
+Settings::~Settings() {
+}
+
+