Hook up link pools in GN.

tools/gn/toolchain.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/toolchain.h"
 
 #include <string.h>
 
 #include "base/logging.h"
 #include "tools/gn/target.h"
 #include "tools/gn/value.h"
 
 const char* Toolchain::kToolCc = "cc";
 const char* Toolchain::kToolCxx = "cxx";
 const char* Toolchain::kToolObjC = "objc";
 const char* Toolchain::kToolObjCxx = "objcxx";
 const char* Toolchain::kToolRc = "rc";
 const char* Toolchain::kToolAsm = "asm";
 const char* Toolchain::kToolAlink = "alink";
 const char* Toolchain::kToolSolink = "solink";
 const char* Toolchain::kToolLink = "link";
 const char* Toolchain::kToolStamp = "stamp";
 const char* Toolchain::kToolCopy = "copy";
 
 Toolchain::Toolchain(const Settings* settings, const Label& label)
     : Item(settings, label),
+      concurrent_links_(0),
       setup_complete_(false) {
 }
 
 Toolchain::~Toolchain() {
 }
 
 Toolchain* Toolchain::AsToolchain() {
   return this;
 }
 
@@ skipping 111 matching lines @@
       return TYPE_STAMP;
     default:
       NOTREACHED();
       return Toolchain::TYPE_NONE;
   }
 }
 
 const Tool* Toolchain::GetToolForTargetFinalOutput(const Target* target) const {
   return tools_[GetToolTypeForTargetFinalOutput(target)].get();
 }