ServiceWorker: Bypass SW when the script doesn't have fetch handler

When the script doesn't have a fetch handler, a request
will immediately go to the network after passed to SW in current implementation.
However, if SW is down, this procedure will wait for waking SW up though SW
doesn't have fetch handler. This patch enables the request to directly go to
network bypassing SW in this situation.

TEST=/out/Release/content_unittest --gtest_filter="ServiceWorkerControlleeRequestHandlerTest.FallbackWithNoFetchHandler"

Cr-Commit-Position: refs/heads/master@{#396787}
3 files changed