Web MIDI: implement implicit open() on send() and setOnmidimessage()

Source/modules/webmidi/MIDIOutput.cpp

Index: Source/modules/webmidi/MIDIOutput.cpp
diff --git a/Source/modules/webmidi/MIDIOutput.cpp b/Source/modules/webmidi/MIDIOutput.cpp
index 5d641b98f5200742889c1f42848af7fb251f64ff..94fffbcac1c7127addc9905a9fcc7315af730afc 100644
--- a/Source/modules/webmidi/MIDIOutput.cpp
+++ b/Source/modules/webmidi/MIDIOutput.cpp
@@ -197,6 +197,10 @@ void MIDIOutput::send(DOMUint8Array* array, double timestamp, ExceptionState& ex
     if (timestamp == 0.0)
         timestamp = now(executionContext());
 
+    // Implicit open. It does nothing if the port is already opened.
+    // This should be performed even if |array| is invalid.
+    open();
+
     if (!array)
         return;