Implement IDBVersionChangeEvent ctor w/ IDBVersionChangeEventInit dict

LayoutTests/storage/indexeddb/event-init-expected.txt

Index: LayoutTests/storage/indexeddb/event-init-expected.txt
diff --git a/LayoutTests/storage/indexeddb/event-init-expected.txt b/LayoutTests/storage/indexeddb/event-init-expected.txt
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index 0000000000000000000000000000000000000000..037d893131aa7aed2a80d58db5b13ff852c672dc
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+++ b/LayoutTests/storage/indexeddb/event-init-expected.txt
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+Verify the use of IDBVersionChangeEventInit
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+event = new IDBVersionChangeEvent('default')
+PASS event instanceof IDBVersionChangeEvent is true
+PASS event.type is "default"
+PASS event.oldVersion is 0
+PASS event.newVersion is null
+
+initEvent = {oldVersion: 123, newVersion: 456}
+event = new IDBVersionChangeEvent('foo', initEvent)
+PASS event instanceof IDBVersionChangeEvent is true
+PASS event.type is "foo"
+PASS event.oldVersion is initEvent.oldVersion
+PASS event.newVersion is initEvent.newVersion
+
+initEvent = {oldVersion: 'legacy', newVersion: null}
+event = new IDBVersionChangeEvent('bar', initEvent)
+PASS event instanceof IDBVersionChangeEvent is true
+PASS event.type is "bar"
+PASS event.oldVersion is 0
+PASS event.newVersion is null
+PASS successfullyParsed is true
+
+TEST COMPLETE
+