Add "create_bundle" target in order to support bundle with gn.

tools/gn/ninja_create_bundle_target_writer.h

Index: tools/gn/ninja_create_bundle_target_writer.h
diff --git a/tools/gn/ninja_create_bundle_target_writer.h b/tools/gn/ninja_create_bundle_target_writer.h
new file mode 100644
index 0000000000000000000000000000000000000000..42b900f6bc2a0ff98f67abd4bf09f89cff9c3f98
--- /dev/null
+++ b/tools/gn/ninja_create_bundle_target_writer.h
@@ -0,0 +1,23 @@
+// 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.
+
+#ifndef TOOLS_GN_NINJA_CREATE_BUNDLE_TARGET_WRITER_H_
+#define TOOLS_GN_NINJA_CREATE_BUNDLE_TARGET_WRITER_H_
+
+#include "base/macros.h"
+#include "tools/gn/ninja_target_writer.h"
+
+// Writes a .ninja file for a bundle_data target type.
+class NinjaCreateBundleTargetWriter : public NinjaTargetWriter {
+ public:
+  NinjaCreateBundleTargetWriter(const Target* target, std::ostream& out);
+  ~NinjaCreateBundleTargetWriter() override;
+
+  void Run() override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(NinjaCreateBundleTargetWriter);
+};
+
+#endif  // TOOLS_GN_NINJA_CREATE_BUNDLE_TARGET_WRITER_H_