CaptureHandleChangeEvent.captureHandle() when navigating

[eladalon1983]

The spec currently reads:

CaptureHandleChangeEvent.captureHandle():

The track's CaptureHandle at the time the event was fired, as observable by the capturing application. If not observable by the capturing application, all of CaptureHandle's fields will be set to their default value - the empty DOMString.

It makes more sense to return the exact same CaptureHandle as would a call to MediaStreamTrack.getCaptureHandle(). When there is no observable CaptureHandle, that means returning null. So:

CaptureHandleChangeEvent.captureHandle():

The track's CaptureHandle at the time the event was fired, as observable by the capturing application. If not observable by the capturing application, returns null, as MediaStreamTrack.getCaptureHandle() does.

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Noteworthy - there's a discussion on issue #50 over a suggestion to strip captureHandle() out of the event altogether. If that proposal is adopted, the current discussion would be rendered moot. However, until we settle that particular discussion, it makes sense to perform a localized fix here.

[eladalon1983]

Rendered irrelevant by other changes. Closing.