Encode the Last-Event-ID header in EventSource as UTF-8.

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

 if (self.importScripts)
     importScripts("/js-test-resources/js-test.js");
 
 description("Test EventSource reconnect after end of event stream.");
 
 self.jsTestIsAsync = true;
 
 var retryTimeout;
 
 function checkReadyState(es, desiredState) {
     shouldBe("es.readyState", "es." + desiredState);
 }
 
 var errCount = 0;
 var es = new EventSource("/eventsource/resources/reconnect.php");
 
 checkReadyState(es, "CONNECTING");
 
 es.onopen = function (evt) {
     checkReadyState(es, "OPEN");
 };
 
 var evt;
 es.onmessage = function (arg) {
     evt = arg;
     if (errCount)
-        shouldBeEqualToString("evt.data", "77");
-    shouldBeEqualToString("evt.lastEventId", "77");
+        shouldBeEqualToString("evt.data", "77\u2603");
+    shouldBeEqualToString("evt.lastEventId", "77\u2603");
 };
 
 es.onerror = function () {
     errCount++;
     if (errCount < 2) {
         checkReadyState(es, "CONNECTING");
         retryTimeout = setTimeout(end, 1000);
         return;
     }
     clearTimeout(retryTimeout);
     retryTimeout = null;
     end();
 };
 
 function end() {
     es.close();
     if (retryTimeout)
         testFailed("did not reconnect in time");
     else
         checkReadyState(es, "CLOSED");
 
     finishJSTest();
 }