Add support for user defined "pool" to GN.

tools/gn/tool.h

 // Copyright 2014 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.
 
 #ifndef TOOLS_GN_TOOL_H_
 #define TOOLS_GN_TOOL_H_
 
 #include <string>
 
 #include "base/logging.h"
 #include "base/macros.h"
+#include "tools/gn/label.h"
+#include "tools/gn/label_ptr.h"
 #include "tools/gn/substitution_list.h"
 #include "tools/gn/substitution_pattern.h"
 
+class Pool;
+
 class Tool {
  public:
   enum DepsFormat {
     DEPS_GCC = 0,
     DEPS_MSVC = 1
   };
 
   enum PrecompiledHeaderType {
     PCH_NONE = 0,
     PCH_GCC = 1,
@@ skipping 141 matching lines @@
   }
 
   const SubstitutionPattern& rspfile_content() const {
     return rspfile_content_;
   }
   void set_rspfile_content(const SubstitutionPattern& content) {
     DCHECK(!complete_);
     rspfile_content_ = content;
   }
 
+  const LabelPtrPair<Pool>& pool() const { return pool_; }
+  void set_pool(const LabelPtrPair<Pool>& pool) { pool_ = pool; }
+
   // Other functions ----------------------------------------------------------
 
   // Called when the toolchain is saving this tool, after everything is filled
   // in.
   void SetComplete();
 
   // Returns true if this tool has separate outputs for dependency tracking
   // and linking.
   bool has_separate_solink_files() const {
     return !link_output_.empty() || !depend_output_.empty();
   }
 
   // Substitutions required by this tool.
   const SubstitutionBits& substitution_bits() const {
     DCHECK(complete_);
     return substitution_bits_;
   }
 
+  bool OnResolved(Err* err);
+
  private:
   SubstitutionPattern command_;
   std::string default_output_extension_;
   SubstitutionPattern default_output_dir_;
   SubstitutionPattern depfile_;
   DepsFormat depsformat_;
   PrecompiledHeaderType precompiled_header_type_;
   SubstitutionPattern description_;
   std::string lib_switch_;
   std::string lib_dir_switch_;
   SubstitutionList outputs_;
   SubstitutionPattern link_output_;
   SubstitutionPattern depend_output_;
   SubstitutionPattern runtime_link_output_;
   std::string output_prefix_;
   bool restat_;
   SubstitutionPattern rspfile_;
   SubstitutionPattern rspfile_content_;
+  LabelPtrPair<Pool> pool_;
 
   bool complete_;
 
   SubstitutionBits substitution_bits_;
 
   DISALLOW_COPY_AND_ASSIGN(Tool);
 };
 
 #endif  // TOOLS_GN_TOOL_H_