Introduce Promises.

Source/core/dom/PromiseResolver.h

Index: Source/core/dom/PromiseResolver.h
diff --git a/Source/modules/webmidi/MIDIErrorCallback.h b/Source/core/dom/PromiseResolver.h
similarity index 86%
copy from Source/modules/webmidi/MIDIErrorCallback.h
copy to Source/core/dom/PromiseResolver.h
index 2684f7bd58b9d03d854c4da09a60386f00039cd7..664018a41bb98e7fd6ccbb8d92c93fdf1b22a0f4 100644
--- a/Source/modules/webmidi/MIDIErrorCallback.h
+++ b/Source/core/dom/PromiseResolver.h
@@ -28,21 +28,19 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef MIDIErrorCallback_h
-#define MIDIErrorCallback_h
+// FIXME: This file should be deleted.
+#ifndef PromiseResolver_h
+#define PromiseResolver_h
 
 #include "wtf/RefCounted.h"
 
 namespace WebCore {
 
-class DOMError;
-
-class MIDIErrorCallback : public RefCounted<MIDIErrorCallback> {
-public:
-    virtual ~MIDIErrorCallback() { }
-    virtual bool handleEvent(DOMError*) = 0;
+// An empty class. This is here because a generated file use it.
+class PromiseResolver : public RefCounted<PromiseResolver> {
 };
 
 } // namespace WebCore
 
-#endif // MIDIErrorCallback_h
+
+#endif // PromiseResolver_h