Add the concept of a source set to GN.

tools/gn/ninja_target_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_target_writer.h"
 
 #include <fstream>
 #include <sstream>
 
 #include "base/file_util.h"
@@ skipping 61 matching lines @@
     NinjaCopyTargetWriter writer(target, file);
     writer.Run();
   } else if (target->output_type() == Target::CUSTOM) {
     NinjaScriptTargetWriter writer(target, file);
     writer.Run();
   } else if (target->output_type() == Target::GROUP) {
     NinjaGroupTargetWriter writer(target, file);
     writer.Run();
   } else if (target->output_type() == Target::EXECUTABLE ||
              target->output_type() == Target::STATIC_LIBRARY ||
-             target->output_type() == Target::SHARED_LIBRARY) {
+             target->output_type() == Target::SHARED_LIBRARY ||
+             target->output_type() == Target::SOURCE_SET) {
     NinjaBinaryTargetWriter writer(target, file);
     writer.Run();
   } else {
     CHECK(0);
   }
 
   std::string contents = file.str();
   file_util::WriteFile(ninja_file, contents.c_str(),
                        static_cast<int>(contents.size()));
 }
@@ skipping 39 matching lines @@
   const Target::FileList& outputs = target_->script_values().outputs();
   std::vector<std::string> output_template_args;
   for (size_t i = 0; i < outputs.size(); i++) {
     // All outputs should be in the output dir.
     output_template_args.push_back(
         RemovePrefix(outputs[i].value(),
                      settings_->build_settings()->build_dir().value()));
   }
   return FileTemplate(output_template_args);
 }