Add "bundle_data" target as first step for adding bundle support to gn.

tools/gn/action_values.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/action_values.h"
 
 #include "tools/gn/settings.h"
 #include "tools/gn/substitution_writer.h"
 #include "tools/gn/target.h"
 
 ActionValues::ActionValues() : console_(false) {}
 
 ActionValues::~ActionValues() {}
 
 void ActionValues::GetOutputsAsSourceFiles(
     const Target* target,
     std::vector<SourceFile>* result) const {
-  if (target->output_type() == Target::COPY_FILES ||
+  if (target->output_type() == Target::BUNDLE_DATA) {
+    // The bundle_data target has no output, the real output will be generated
+    // by the create_bundle target.
+  } else if (target->output_type() == Target::COPY_FILES ||
       target->output_type() == Target::ACTION_FOREACH) {
     // Copy and foreach applies the outputs to the sources.
     SubstitutionWriter::ApplyListToSources(
         target->settings(), outputs_, target->sources(), result);
   } else {
     // Actions (and anything else that happens to specify an output) just use
     // the output list with no substitution.
     SubstitutionWriter::GetListAsSourceFiles(outputs_, result);
   }
 }