Make gn check //mojo/public/* pass

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",
-    "callback.h",
     "error_handler.h",
     "interface_ptr.h",
     "message.h",
     "message_filter.h",
     "no_interface.h",
     "string.h",
     "struct_ptr.h",
     "type_converter.h",
     "lib/array_internal.cc",
     "lib/array_internal.h",
     "lib/array_serialization.h",
     "lib/bindings_internal.h",
     "lib/bindings_serialization.cc",
     "lib/bindings_serialization.h",
     "lib/bounds_checker.cc",
     "lib/bounds_checker.h",
     "lib/buffer.h",
-    "lib/callback_internal.h",
     "lib/connector.cc",
     "lib/connector.h",
     "lib/filter_chain.cc",
     "lib/filter_chain.h",
     "lib/fixed_buffer.cc",
     "lib/fixed_buffer.h",
     "lib/message.cc",
     "lib/message_builder.cc",
     "lib/message_builder.h",
     "lib/message_filter.cc",
     "lib/message_header_validator.cc",
     "lib/message_header_validator.h",
     "lib/message_internal.h",
     "lib/message_queue.cc",
     "lib/message_queue.h",
     "lib/no_interface.cc",
     "lib/router.cc",
     "lib/router.h",
-    "lib/shared_data.h",
-    "lib/shared_ptr.h",
     "lib/string_serialization.cc",
     "lib/string_serialization.h",
-    "lib/template_util.h",
     "lib/validation_errors.cc",
     "lib/validation_errors.h",
   ]
+
+  deps = [
+    ":callback",
+    "//mojo/public/cpp/environment",
+    "//mojo/public/cpp/system",
+  ]
 }
+
+source_set("callback") {
+  sources = [
+    "callback.h",
+    "lib/callback_internal.h",
+    "lib/template_util.h",
+    "lib/shared_data.h",
+    "lib/shared_ptr.h",
+  ]
+
+  deps = [ "//mojo/public/cpp/system" ]
+}