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

tools/gn/BUILD.gn

Index: tools/gn/BUILD.gn
diff --git a/tools/gn/BUILD.gn b/tools/gn/BUILD.gn
index b27ae70f0d586920d9ede9b271a82d2bd877dc77..37bce8d89035705820edc6e528ee26cc723b256b 100644
--- a/tools/gn/BUILD.gn
+++ b/tools/gn/BUILD.gn
@@ -24,8 +24,12 @@ static_library("gn_lib") {
     "builder.h",
     "builder_record.cc",
     "builder_record.h",
+    "bundle_data.cc",
+    "bundle_data.h",
     "bundle_data_target_generator.cc",
     "bundle_data_target_generator.h",
+    "bundle_file_rule.cc",
+    "bundle_file_rule.h",
     "c_include_iterator.cc",
     "c_include_iterator.h",
     "command_args.cc",
@@ -50,6 +54,8 @@ static_library("gn_lib") {
     "config_values_generator.h",
     "copy_target_generator.cc",
     "copy_target_generator.h",
+    "create_bundle_target_generator.cc",
+    "create_bundle_target_generator.h",
     "deps_iterator.cc",
     "deps_iterator.h",
     "eclipse_writer.cc",
@@ -116,6 +122,8 @@ static_library("gn_lib") {
     "ninja_bundle_data_target_writer.h",
     "ninja_copy_target_writer.cc",
     "ninja_copy_target_writer.h",
+    "ninja_create_bundle_target_writer.cc",
+    "ninja_create_bundle_target_writer.h",
     "ninja_group_target_writer.cc",
     "ninja_group_target_writer.h",
     "ninja_target_writer.cc",
@@ -278,6 +286,7 @@ test("gn_unittests") {
     "ninja_action_target_writer_unittest.cc",
     "ninja_binary_target_writer_unittest.cc",
     "ninja_copy_target_writer_unittest.cc",
+    "ninja_create_bundle_target_writer_unittest.cc",
     "ninja_group_target_writer_unittest.cc",
     "ninja_target_writer_unittest.cc",
     "ninja_toolchain_writer_unittest.cc",