Allow dependencies of toolchains in GN.

tools/gn/toolchain.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_TOOLCHAIN_H_
 #define TOOLS_GN_TOOLCHAIN_H_
 
 #include "base/compiler_specific.h"
 #include "base/strings/string_piece.h"
 #include "tools/gn/item.h"
+#include "tools/gn/label_ptr.h"
 #include "tools/gn/scope.h"
 #include "tools/gn/value.h"
 
 // Holds information on a specific toolchain. This data is filled in when we
 // encounter a toolchain definition.
 //
 // This class is an Item so it can participate in dependency management. In
 // particular, when a target uses a toolchain, it should have a dependency on
 // that toolchain's object so that we can be sure we loaded the toolchain
 // before generating the build for that target.
@@ skipping 56 matching lines @@
   virtual Toolchain* AsToolchain() OVERRIDE;
   virtual const Toolchain* AsToolchain() const OVERRIDE;
 
   // Returns TYPE_NONE on failure.
   static ToolType ToolNameToType(const base::StringPiece& str);
   static std::string ToolTypeToName(ToolType type);
 
   const Tool& GetTool(ToolType type) const;
   void SetTool(ToolType type, const Tool& t);
 
+  // Targets that must be resolved before compiling any targets.
+  const LabelTargetVector& deps() const { return deps_; }
+  LabelTargetVector& deps() { return deps_; }
+
   // Specifies build argument overrides that will be set on the base scope. It
   // will be as if these arguments were passed in on the command line. This
   // allows a toolchain to override the OS type of the default toolchain or
   // pass in other settings.
   Scope::KeyValueMap& args() { return args_; }
   const Scope::KeyValueMap& args() const { return args_; }
 
  private:
   Tool tools_[TYPE_NUMTYPES];
 
+  LabelTargetVector deps_;
   Scope::KeyValueMap args_;
 };
 
 #endif  // TOOLS_GN_TOOLCHAIN_H_