ServiceWorker: Change worker script fetch error code.

Change worker script fetch error code in "Update" algorithm to align
with spec:
Non 2xx response will be rejected with NetworkError;
Redirected response will be rejected with SecurityError;
Reponse with Wrong MIME type will be rejected with SecurityError.

(1/3): this.
(2/3): https://codereview.chromium.org/567903002/
(3/3): Layout test & Blink side cleanup

BUG=408421
TEST=http/tests/serviceworker

Review URL: https://codereview.chromium.org/546353003

git-svn-id: svn://svn.chromium.org/blink/trunk@182381 bbb929c8-8fbe-4397-9dbb-9b2b20218538