WIP don't review: Implement Future

Source/core/dom/FutureResolver.idl

Index: Source/core/dom/FutureResolver.idl
diff --git a/Source/modules/webmidi/MIDIErrorCallback.idl b/Source/core/dom/FutureResolver.idl
similarity index 91%
copy from Source/modules/webmidi/MIDIErrorCallback.idl
copy to Source/core/dom/FutureResolver.idl
index 0591bf6715e14bf85426c3cfb82fc2aedf25918d..913c4196ba1a2671ff7384f682a09ee823925e82 100644
--- a/Source/modules/webmidi/MIDIErrorCallback.idl
+++ b/Source/core/dom/FutureResolver.idl
@@ -28,6 +28,8 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-callback interface MIDIErrorCallback {
-    boolean handleEvent(DOMError error);
+interface FutureResolver {
+    void accept(optional any value);
+    [Custom] void resolve(optional any value);
+    void reject(optional any value);
 };