Mojo: Simplify typemap usage.

mojo/public/cpp/bindings/BUILD.gn

 # Copyright 2014 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.
 
 source_set("bindings") {
   sources = [
     "array.h",
     "associated_binding.h",
     "associated_group.h",
     "associated_interface_ptr.h",
@@ skipping 78 matching lines @@
     # serialization_forward.h.
     "lib/wtf_string_serialization.h",
     "map.h",
     "message.h",
     "message_filter.h",
     "no_interface.h",
     "stl_converters.h",
     "string.h",
     "strong_binding.h",
     "struct_ptr.h",
-    "struct_traits.h",
     "type_converter.h",
   ]
 
   public_deps = [
     ":callback",
+    ":struct_traits",
     "//base",
     "//ipc:param_traits",
     "//mojo/public/cpp/system",
   ]
 
   deps = [
     "//base",
     "//mojo/public/interfaces/bindings:bindings_cpp_sources",
   ]
 }
 
 source_set("callback") {
   sources = [
     "callback.h",
     "lib/callback_internal.h",
     "lib/shared_data.h",
     "lib/shared_ptr.h",
     "lib/template_util.h",
   ]
 
   deps = [
     "//base",
     "//mojo/public/cpp/system",
   ]
 }
 
+source_set("struct_traits") {
+  sources = [
+    "struct_traits.h",
+  ]
+}
+
 source_set("wtf_support") {
   sources = [
     "lib/wtf_array_serialization.h",
     "lib/wtf_serialization.h",
     "lib/wtf_string_serialization.cc",
     "lib/wtf_string_serialization.h",
     "wtf_array.h",
   ]
 
   public_deps = [
     ":bindings",
     "//third_party/WebKit/Source/wtf",
   ]
 
   public_configs = [ "//third_party/WebKit/Source:config" ]
 }