Update ServiceWorkerClientTest CTS test to make sure SW is unregistered.

Make sure to do a proper clean-up by unregistering the Service
Worker in the end of the CTS test to avoid potential clashes
during re-runs. The test now also checks that the Service Worker
can be sucessfully unregistered.
(crbug.com/675809)

CRBUG=675809
Test: cts-tradefed run cts -m CtsWebkitTestCases --test android.webkit.cts.ServiceWorkerClientTest

Change-Id: I548eee079281a1bd6d183d3df61414abf1e890e6
Merged-In: I5584935472bb6c936b9bace4f2f393d972a9151d
1 file changed