Web MIDI: introduce WebMIDIClient API to request a permission

Source/core/platform/midi/MIDIAccessor.h

Index: Source/core/platform/midi/MIDIAccessor.h
diff --git a/Source/core/platform/midi/MIDIAccessor.h b/Source/core/platform/midi/MIDIAccessor.h
index 3eaa90c9362c42f9c96afcdd857b3607f6732c32..39dd88db1612d3a89c4e06f3bf9d71a73749bfc9 100644
--- a/Source/core/platform/midi/MIDIAccessor.h
+++ b/Source/core/platform/midi/MIDIAccessor.h
@@ -46,18 +46,19 @@ public:
 
     virtual ~MIDIAccessor() { }
 
-    void requestAccess(bool access);
+    void startSession();
     void sendMIDIData(unsigned portIndex, const unsigned char* data, size_t length, double timeStamp);
 
     // WebKit::WebMIDIAccessorClient
     virtual void didAddInputPort(const WebKit::WebString& id, const WebKit::WebString& manufacturer, const WebKit::WebString& name, const WebKit::WebString& version) OVERRIDE;
     virtual void didAddOutputPort(const WebKit::WebString& id, const WebKit::WebString& manufacturer, const WebKit::WebString& name, const WebKit::WebString& version) OVERRIDE;
+    virtual void didStartSession() OVERRIDE;
     virtual void didAllowAccess() OVERRIDE;
     virtual void didBlockAccess() OVERRIDE;
     virtual void didReceiveMIDIData(unsigned portIndex, const unsigned char* data, size_t length, double timeStamp) OVERRIDE;
 
 private:
-    MIDIAccessor(MIDIAccessorClient*);
+    explicit MIDIAccessor(MIDIAccessorClient*);
 
     MIDIAccessorClient* m_client;
     OwnPtr<WebKit::WebMIDIAccessor> m_accessor;