Move MIDI code to hang off WebFrame.

public/web/WebFrameClient.h

Index: public/web/WebFrameClient.h
diff --git a/public/web/WebFrameClient.h b/public/web/WebFrameClient.h
index 997c64491804c3ecf5ee454245b998fac5bbe2de..a4fb1ee9983e7c996726a88a07a57b556da335b3 100644
--- a/public/web/WebFrameClient.h
+++ b/public/web/WebFrameClient.h
@@ -67,6 +67,7 @@ class WebGeolocationClient;
 class WebInputEvent;
 class WebMediaPlayer;
 class WebMediaPlayerClient;
+class WebMIDIClient;
 class WebNotificationPresenter;
 class WebServiceWorkerProvider;
 class WebServiceWorkerProviderClient;
@@ -464,6 +465,11 @@ public:
     virtual WebUserMediaClient* userMediaClient() { return 0; }
 
 
+    // Web MIDI -------------------------------------------------------------
+
+    virtual WebMIDIClient* webMIDIClient() { return 0; }
+
+
     // Messages ------------------------------------------------------
 
     // Notifies the embedder that a postMessage was issued on this frame, and