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

tools/gn/ninja_bundle_data_target_writer.cc

+// Copyright 2016 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_bundle_data_target_writer.h"
+
+#include "tools/gn/output_file.h"
+
+NinjaBundleDataTargetWriter::NinjaBundleDataTargetWriter(const Target* target,
+                                                         std::ostream& out)
+    : NinjaTargetWriter(target, out) {}
+
+NinjaBundleDataTargetWriter::~NinjaBundleDataTargetWriter() {}
+
+void NinjaBundleDataTargetWriter::Run() {
+  std::vector<OutputFile> files;
+  files.push_back(WriteInputDepsStampAndGetDep(std::vector<const Target*>()));
+  WriteStampForTarget(files, std::vector<OutputFile>());
+}