Web MIDI: add blink APIs to notify device connection events

public/platform/WebMIDIAccessorClient.h

Index: public/platform/WebMIDIAccessorClient.h
diff --git a/public/platform/WebMIDIAccessorClient.h b/public/platform/WebMIDIAccessorClient.h
index 0192a798a35ae6b898a3c01856ef3a75f4811edb..81d2a2cceb04bd655242485becf2462e9aaab58c 100644
--- a/public/platform/WebMIDIAccessorClient.h
+++ b/public/platform/WebMIDIAccessorClient.h
@@ -37,9 +37,17 @@ namespace blink {
 
 class WebMIDIAccessorClient {
 public:
+    // FIXME: Remove deprecated interfaces that do not have |active| argument.
     virtual void didAddInputPort(const WebString& id, const WebString& manufacturer, const WebString& name, const WebString& version) = 0;
     virtual void didAddOutputPort(const WebString& id, const WebString& manufacturer, const WebString& name, const WebString& version) = 0;
 
+    // didAddInputPort() and didAddOutputPort() can be called before and after didStartSession() is called. But |id| should be unique in each function.

[tkent, 2014/10/20 05:54:07]

nit: I recommend to wrap code comments in 80 columns.

[Takashi Toyoshima, 2014/10/20 06:24:18]

Done.

+    virtual void didAddInputPort(const WebString& id, const WebString& manufacturer, const WebString& name, const WebString& version, bool active) = 0;
+    virtual void didAddOutputPort(const WebString& id, const WebString& manufacturer, const WebString& name, const WebString& version, bool active) = 0;
+    // didSetInputPortState() and didSetOutputPortState() should not be called until didStartSession() is called.
+    virtual void didSetInputPortState(unsigned portIndex, bool active) = 0;
+    virtual void didSetOutputPortState(unsigned portIndex, bool active) = 0;
+
     virtual void didStartSession(bool success, const WebString& error, const WebString& message) = 0;
 
     // |timeStamp| is in milliseconds according to the Web MIDI API.