[WebMIDI] Fix a WebMIDIPermissionRequest leak.

content/renderer/media/midi_dispatcher.h

Index: content/renderer/media/midi_dispatcher.h
diff --git a/content/renderer/media/midi_dispatcher.h b/content/renderer/media/midi_dispatcher.h
index 1e6c8e3937707b94ac2f6e6acae95d941e09460a..3b4cd4f2a720f976cdf6b7e9a87984ce5878fed1 100644
--- a/content/renderer/media/midi_dispatcher.h
+++ b/content/renderer/media/midi_dispatcher.h
@@ -44,7 +44,8 @@ class MidiDispatcher : public RenderViewObserver,
   // Each WebMIDIPermissionRequest object is valid until
   // cancelSysexPermissionRequest() is called with the object, or used to call
   // WebMIDIPermissionRequest::setIsAllowed().
-  IDMap<blink::WebMIDIPermissionRequest> requests_;
+  typedef IDMap<blink::WebMIDIPermissionRequest, IDMapOwnPointer> Requests;
+  Requests requests_;
 
   DISALLOW_COPY_AND_ASSIGN(MidiDispatcher);
 };