Rework EventSource tests for better Worker test coverage.

LayoutTests/http/tests/eventsource/script-tests/eventsource-bad-mime-type.js

Index: LayoutTests/http/tests/eventsource/script-tests/eventsource-bad-mime-type.js
diff --git a/LayoutTests/http/tests/eventsource/script-tests/eventsource-bad-mime-type.js b/LayoutTests/http/tests/eventsource/script-tests/eventsource-bad-mime-type.js
new file mode 100644
index 0000000000000000000000000000000000000000..8ea0ab85974edf24ec8354d83aeb9a7e4b8b3e41
--- /dev/null
+++ b/LayoutTests/http/tests/eventsource/script-tests/eventsource-bad-mime-type.js
@@ -0,0 +1,27 @@
+if (self.importScripts)
+    importScripts("/js-test-resources/js-test.js");
+
+description("Test EventSource with an event-stream with incorrect mime-type.");
+
+self.jsTestIsAsync = true;
+
+function end() {
+    es.close();
+    finishJSTest();
+}
+
+var es = new EventSource("resources/bad-mime-type.asis");
+es.onopen = function (evt) {
+    testFailed("got unexpected open event");
+    end();
+};
+
+es.onmessage = function (evt) {
+    testFailed("got unexpected message event");
+    end();
+};
+
+es.onerror = function () {
+    shouldBe("es.readyState", "es.CLOSED");
+    end();
+};