Add support for user defined "pool" to GN.

tools/gn/builder.h

 // 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.
 
 #ifndef TOOLS_GN_BUILDER_H_
 #define TOOLS_GN_BUILDER_H_
 
 #include "base/callback.h"
 #include "base/containers/hash_tables.h"
 #include "base/macros.h"
@@ skipping 101 matching lines @@
   // This takes a BuilderRecord with resolved depdencies, and fills in the
   // target's Label*Vectors with the resolved pointers.
   bool ResolveItem(BuilderRecord* record, Err* err);
 
   // Fills in the pointers in the given vector based on the labels. We assume
   // that everything should be resolved by this point, so will return an error
   // if anything isn't found or if the type doesn't match.
   bool ResolveDeps(LabelTargetVector* deps, Err* err);
   bool ResolveConfigs(UniqueVector<LabelConfigPair>* configs, Err* err);
   bool ResolveToolchain(Target* target, Err* err);
+  bool ResolvePools(Toolchain* toolchain, Err* err);
 
   // Given a list of unresolved records, tries to find any circular
   // dependencies and returns the string describing the problem. If no circular
   // deps were found, returns the empty string.
   std::string CheckForCircularDependencies(
       const std::vector<const BuilderRecord*>& bad_records) const;
 
   // Non owning pointer.
   Loader* loader_;
 
   // Owning pointers.
   typedef base::hash_map<Label, BuilderRecord*> RecordMap;
   RecordMap records_;
 
   ResolvedCallback resolved_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(Builder);
 };
 
 #endif  // TOOLS_GN_BUILDER_H_