Rework EventSource tests for better Worker test coverage.

LayoutTests/http/tests/eventsource/script-tests/eventsource-eof.js

+if (self.importScripts)
+    importScripts("/js-test-resources/js-test.js");
+
+description("Test that EventSource discards event data if there is no newline before eof.");
+
+self.jsTestIsAsync = true;
+
+var count = 1;
+
+var es = new EventSource("/eventsource/resources/es-eof.php");
+
+es.onerror = function () {
+    if (count++ == 3) {
+        es.close();
+        finishJSTest();
+    }
+};
+
+var evt;
+
+es.onmessage = function (arg) {
+    evt = arg;
+    if (evt.data == ("DATA" + count)) {
+        shouldBeEqualToString("evt.type", "message");
+        shouldBeEqualToString("evt.data", "DATA" + count);
+        shouldBeEqualToString("evt.lastEventId", count.toString());
+        return;
+    }
+    shouldBeEqualToString("evt.type", "msg");
+    shouldBeEqualToString("evt.data", "DATA");
+    shouldBeEqualToString("evt.lastEventId", "3.1");
+};
+es.addEventListener("msg", es.onmessage);