Add support for user defined "pool" to GN.

tools/gn/ninja_toolchain_writer.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/ninja_toolchain_writer.h"
 
 #include <fstream>
 
 #include "base/files/file_util.h"
 #include "base/strings/stringize_macros.h"
 #include "tools/gn/build_settings.h"
 #include "tools/gn/filesystem_utils.h"
 #include "tools/gn/ninja_utils.h"
+#include "tools/gn/pool.h"
 #include "tools/gn/settings.h"
 #include "tools/gn/substitution_writer.h"
 #include "tools/gn/target.h"
 #include "tools/gn/toolchain.h"
 #include "tools/gn/trace.h"
 
 namespace {
 
 const char kIndent[] = "  ";
 
@@ skipping 82 matching lines @@
     // MSVC deps don't have a depfile.
     out_ << kIndent << "deps = msvc" << std::endl;
   }
 
   // The link pool applies to linker tools. Don't count TYPE_ALINK since
   // static libraries are not generally intensive to write.
   if (type == Toolchain::TYPE_SOLINK ||
       type == Toolchain::TYPE_SOLINK_MODULE ||
       type == Toolchain::TYPE_LINK) {
     out_ << kIndent << "pool = link_pool\n";
+  } else if (tool->pool().ptr) {
+    std::string pool_name =
+        tool->pool().ptr->GetNinjaName(settings_->default_toolchain_label());
+    out_ << kIndent << "pool = " << pool_name << std::endl;
   }
 
   if (tool->restat())
     out_ << kIndent << "restat = 1" << std::endl;
 }
 
 void NinjaToolchainWriter::WriteRulePattern(const char* name,
                                             const SubstitutionPattern& pattern,
                                             const EscapeOptions& options) {
   if (pattern.empty())
     return;
   out_ << kIndent << name << " = ";
   SubstitutionWriter::WriteWithNinjaVariables(pattern, options, out_);
   out_ << std::endl;
 }
 
 void NinjaToolchainWriter::WriteSubninjas() {
   // Write subninja commands for each generated target.
   for (const auto& target : targets_) {
     OutputFile ninja_file(target->settings()->build_settings(),
                           GetNinjaFileForTarget(target));
     out_ << "subninja ";
     path_output_.WriteFile(out_, ninja_file);
     out_ << std::endl;
   }
   out_ << std::endl;
 }