Make //mojo/edk/js a component.

mojo/edk/js/threading.h

 // Copyright 2013 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 MOJO_EDK_JS_THREADING_H_
 #define MOJO_EDK_JS_THREADING_H_
 
 #include "gin/public/wrapper_info.h"
+#include "mojo/edk/js/js_export.h"
 #include "v8/include/v8.h"
 
 namespace mojo {
 namespace edk {
 namespace js {
 
-class Threading {
+class MOJO_JS_EXPORT Threading {
  public:
   static const char kModuleName[];
   static v8::Local<v8::Value> GetModule(v8::Isolate* isolate);
  private:
   Threading();
 };
 
 }  // namespace js
 }  // namespace edk
 }  // namespace mojo
 
 #endif  // MOJO_EDK_JS_THREADING_H_