Web MIDI: introduce WebMIDIClient API to request a permission

Source/modules/webmidi/MIDIAccess.h

Index: Source/modules/webmidi/MIDIAccess.h
diff --git a/Source/modules/webmidi/MIDIAccess.h b/Source/modules/webmidi/MIDIAccess.h
index 595afceabf03f5a2aa90ec187998a4bdfa0e3877..8c332c34734b3178d392ed9f6005929770908bf7 100644
--- a/Source/modules/webmidi/MIDIAccess.h
+++ b/Source/modules/webmidi/MIDIAccess.h
@@ -45,6 +45,7 @@
 namespace WebCore {
 
 class ScriptExecutionContext;
+class SecurityOrigin;
 class MIDIAccessPromise;
 
 class MIDIAccess : public RefCounted<MIDIAccess>, public ScriptWrappable, public ActiveDOMObject, public EventTarget, public MIDIAccessorClient {
@@ -70,6 +71,8 @@ public:
     virtual void stop();
 
     // MIDIAccessorClient
+    SecurityOrigin* securityOrigin() const OVERRIDE;
+
     virtual void didAddInputPort(const String& id, const String& manufacturer, const String& name, const String& version) OVERRIDE;
     virtual void didAddOutputPort(const String& id, const String& manufacturer, const String& name, const String& version) OVERRIDE;
     virtual void didAllowAccess() OVERRIDE;