Inherit EventTarget interface instead of duplicating its code

LayoutTests/webexposed/event-target-in-prototype-expected.txt

Index: LayoutTests/webexposed/event-target-in-prototype-expected.txt
diff --git a/LayoutTests/webexposed/event-target-in-prototype-expected.txt b/LayoutTests/webexposed/event-target-in-prototype-expected.txt
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index 0000000000000000000000000000000000000000..de47cc82c57e56f6040f669790bbd1bbd2e98c08
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+++ b/LayoutTests/webexposed/event-target-in-prototype-expected.txt
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+Check that interfaces inherit from EventTarget
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+PASS EventSource.prototype.__proto__ is EventTarget.prototype
+PASS MessagePort.prototype.__proto__ is EventTarget.prototype
+FAIL Node.prototype.__proto__ should be [object Object]. Was [object Object].
+PASS WebSocket.prototype.__proto__ is EventTarget.prototype
+FAIL Window.prototype.__proto__ should be [object Object]. Was [object Object].
+PASS XMLHttpRequest.prototype.__proto__ is EventTarget.prototype
+PASS XMLHttpRequestUpload.prototype.__proto__ is EventTarget.prototype
+PASS webkitAudioContext.prototype.__proto__ is EventTarget.prototype
+PASS successfullyParsed is true
+
+TEST COMPLETE
+