[cssom-view] Screen interface has extra stuff in browsers

In adding IDL tests for CSSOM View in https://github.com/w3c/web-platform-tests/pull/6982 I noticed that Gecko failed just two tests, because it has Screen inheriting from EventTarget. Which made me curious.

http://software.hixie.ch/utilities/js/live-dom-viewer/saved/5324

In Gecko (Firefox Nightly), iterating screen gives:

log: mozLockOrientation: function mozLockOrientation() {
    [native code]
}
log: mozUnlockOrientation: function mozUnlockOrientation() {
    [native code]
}
log: availWidth: 1680
log: availHeight: 1024
log: width: 1680
log: height: 1050
log: colorDepth: 24
log: pixelDepth: 24
log: top: 0
log: left: 0
log: availTop: 22
log: availLeft: 0
log: mozOrientation: landscape-primary
log: onmozorientationchange: null
log: orientation: [object ScreenOrientation]
log: addEventListener: function addEventListener() {
    [native code]
}
log: removeEventListener: function removeEventListener() {
    [native code]
}
log: dispatchEvent: function dispatchEvent() {
    [native code]
}

Chromium (Chrome Canary):

log: availWidth: 1680
log: availHeight: 1024
log: width: 1680
log: height: 1050
log: colorDepth: 24
log: pixelDepth: 24
log: availLeft: 0
log: availTop: 22
log: orientation: [object ScreenOrientation]
log: keepAwake: false

WebKit (Safari TP) has just the specified members:

log: height: 1050
log: width: 1680
log: colorDepth: 24
log: pixelDepth: 24
log: availLeft: 0
log: availTop: 22
log: availHeight: 1024
log: availWidth: 1680

EdgeHTML 15 (via browserstack):

log: availHeight: 950
log: availWidth: 1680
log: bufferDepth: 0
log: colorDepth: 0
log: deviceXDPI: 96
log: deviceYDPI: 96
log: fontSmoothingEnabled: true
log: height: 1536
log: logicalXDPI: 96
log: logicalYDPI: 96
log: msOrientation: landscape-primary
log: onmsorientationchange: null
log: pixelDepth: 24
log: systemXDPI: 96
log: systemYDPI: 96
log: width: 2048
log: msLockOrientation: function msLockOrientation() { [native code] }
log: msUnlockOrientation: function msUnlockOrientation() { [native code] }
log: addEventListener: function addEventListener() { [native code] }
log: dispatchEvent: function dispatchEvent() { [native code] }
log: removeEventListener: function removeEventListener() { [native code] }

screen.orientation is https://w3c.github.io/screen-orientation/

What do we want to do with the other stuff? Standardize? Try to remove from browsers?