Add Client Attribute to FetchEvent- Blink Side.

LayoutTests/http/tests/serviceworker/resources/fetch-event-client-attribute-test-worker.js

+self.addEventListener('fetch', function(event) {
+    event.respondWith(new Response((event.client.frameType).toString()));

[jsbell, 2015/05/05 17:45:42]

The only assertion in the test is looking at data.expected and data.actual;
since the message data here is a string, both of those will be undefined, and so
pass. So this is not actually validating anything.

[Paritosh Kumar, 2015/05/06 11:42:36]

We are using an assertion in promise_test as:
assert_equals(frame.contentDocument.body.textContent, "top-level", "frameType
should be top-level");
And this return value will be passed to client frame.

[jsbell, 2015/05/06 16:21:26]

Got it, thanks for the explanation! I was looking at the unused assert.

This makes sense!

+});