Add the concept of a source set to GN.

tools/gn/functions.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_FUNCTIONS_H_
 #define TOOLS_GN_FUNCTIONS_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 176 matching lines @@
                                     Err* err);
 
 extern const char kSharedLibrary[];
 extern const char kSharedLibrary_Help[];
 Value RunSharedLibrary(Scope* scope,
                        const FunctionCallNode* function,
                        const std::vector<Value>& args,
                        BlockNode* block,
                        Err* err);
 
+extern const char kSourceSet[];
+extern const char kSourceSet_Help[];
+Value RunSourceSet(Scope* scope,
+                   const FunctionCallNode* function,
+                   const std::vector<Value>& args,
+                   BlockNode* block,
+                   Err* err);
+
 extern const char kStaticLibrary[];
 extern const char kStaticLibrary_Help[];
 Value RunStaticLibrary(Scope* scope,
                        const FunctionCallNode* function,
                        const std::vector<Value>& args,
                        BlockNode* block,
                        Err* err);
 
 extern const char kTemplate[];
 extern const char kTemplate_Help[];
@@ skipping 119 matching lines @@
 // Returns the name of the toolchain for the given scope.
 const Label& ToolchainLabelForScope(const Scope* scope);
 
 // Generates a label for the given scope, using the current directory and
 // toolchain, and the given name.
 Label MakeLabelForScope(const Scope* scope,
                         const FunctionCallNode* function,
                         const std::string& name);
 
 #endif  // TOOLS_GN_FUNCTIONS_H_