Make WebMIDI use blink Promise.

LayoutTests/webmidi/requestmidiaccess-expected.txt

 Tests navigator.requestMIDIAccess.
 
 On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
 
 
 PASS navigator.requestMIDIAccess().then(successCallback1, errorCallback1) did not throw exception.
 PASS requestMIDIAccess() succeeded with access [object MIDIAccess].
 PASS access.inputs().length is 1
 PASS access.outputs().length is 1
 PASS input attributes are correct
 PASS output attributes are correct
 PASS output.send([0xf1, 0x45, 0x7f]) threw exception SecurityError: Failed to execute 'send' on 'MIDIOutput': permission to send system exclusive messages is denied..
+PASS navigator.requestMIDIAccess({sysex: true}).then(successCallback2, errorCallback2) did not throw exception.

[Takashi Toyoshima, 2013/12/03 10:48:50]

Hum... I'm not sure why this line is changed by this CL.

Anyway I noticed that the following line in the requestmidiaccess.html is wrong
now.
shouldNotThrow("navigator.requestMIDIAccess({sysex:
true}).then(successCallback2, errorCallback2)");

Originally, the method is throwable, but isn't now. Can you remove
'shouldNotThread' from this line?

[yhirano, 2013/12/03 12:14:16]

Maybe it's because Blink Promise calls onFulfill / onReject asynchronously.
I modified tests and expectations.

 PASS requestMIDIAccess() was correctly blocked for System Exclusive access with error [object DOMError].
 PASS successfullyParsed is true
 
 TEST COMPLETE