Improve GN handling of directory templates.

tools/gn/action_values.h

Index: tools/gn/action_values.h
diff --git a/tools/gn/action_values.h b/tools/gn/action_values.h
index 8b883c752016f73703239f522d0af384667f8554..7a70d3311a8339fd34225129461d517ed1fd7298 100644
--- a/tools/gn/action_values.h
+++ b/tools/gn/action_values.h
@@ -25,12 +25,11 @@ class ActionValues {
   // Arguments to the script.
   std::vector<std::string>& args() { return args_; }
   const std::vector<std::string>& args() const { return args_; }
-  void swap_in_args(std::vector<std::string>* a) { args_.swap(*a); }
 
-  // Files created by the script.
-  std::vector<SourceFile>& outputs() { return outputs_; }
-  const std::vector<SourceFile>& outputs() const { return outputs_; }
-  void swap_in_outputs(std::vector<SourceFile>* op) { outputs_.swap(*op); }
+  // Files created by the script. These are strings rather than SourceFiles
+  // since they will often contain {{source expansions}}.
+  std::vector<std::string>& outputs() { return outputs_; }
+  const std::vector<std::string>& outputs() const { return outputs_; }
 
   // Depfile generated by the script.
   const SourceFile& depfile() const { return depfile_; }
@@ -40,7 +39,7 @@ class ActionValues {
  private:
   SourceFile script_;
   std::vector<std::string> args_;
-  std::vector<SourceFile> outputs_;
+  std::vector<std::string> outputs_;
   SourceFile depfile_;
 
   DISALLOW_COPY_AND_ASSIGN(ActionValues);