Add support for user defined "pool" to GN.

tools/gn/pool.cc

+// Copyright 2016 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/pool.h"
+
+#include <sstream>
+
+#include "base/logging.h"
+
+Pool::Pool(const Settings* settings, const Label& label)
+    : Item(settings, label) {}
+
+Pool::~Pool() {}
+
+Pool* Pool::AsPool() {
+  return this;
+}
+
+const Pool* Pool::AsPool() const {
+  return this;
+}
+
+std::string Pool::GetNinjaName(const Label& default_toolchain) const {
+  bool include_toolchain = label().toolchain_dir() != default_toolchain.dir() ||
+                           label().toolchain_name() != default_toolchain.name();
+  return GetNinjaName(include_toolchain);
+}
+
+std::string Pool::GetNinjaName(bool include_toolchain) const {
+  std::ostringstream buffer;
+  if (include_toolchain) {
+    DCHECK(label().toolchain_dir().is_source_absolute());
+    std::string toolchain_dir = label().toolchain_dir().value();
+    for (std::string::size_type i = 2; i < toolchain_dir.size(); ++i) {
+      buffer << (toolchain_dir[i] == '/' ? '_' : toolchain_dir[i]);
+    }
+    buffer << label().toolchain_name() << "_";
+  }
+
+  DCHECK(label().dir().is_source_absolute());
+  std::string label_dir = label().dir().value();
+  for (std::string::size_type i = 2; i < label_dir.size(); ++i) {
+    buffer << (label_dir[i] == '/' ? '_' : label_dir[i]);
+  }
+  buffer << label().name();
+  return buffer.str();
+}