S13nSW: GetControllerServiceWorkerPtr() doesn't ensure the controller is running

The method is similar to EnsureControllerServiceWorker but in some cases we
can't make sure that the controller service worker is running (as existing
comment described). Update the description of the method to state that this
method doesn't guarantee that the controller is running.

The method will be called during navigation when S13nSW is enabled. During
navigation, we need to make sure that the controller is running before
calling this method. Currently we make sure this by calling
ServiceWorkerFetchDispatcher::StartWorker() in the following sequence:

ServiceWorkerControlleeRequestHandler::MaybeCreateLoader()
-> ServiceWorkerURLJobWrapper::ForwardToServiceWorker()
-> ServiceWorkerNavigationLoader::ForwardToServiceWorker()
-> ServiceWorkerFetchDispatcher::Run()
-> ServiceWorkerFetchDispatcher::StartWorker()

After creating a loader, we call GetControllerServiceWorkerPtr() in
ServiceWorkerControlleeReuqestHandler::MaybeCreateSubresourceLoaderParams().

Bug: 797222
Change-Id: If7ef6dbe2e59c15e2f737f16d68f0c851d889556
Reviewed-on: https://chromium-review.googlesource.com/987832
Reviewed-by: Kinuko Yasuda <[email protected]>
Reviewed-by: Matt Falkenhagen <[email protected]>
Commit-Queue: Kenichi Ishibashi <[email protected]>
Cr-Commit-Position: refs/heads/master@{#547634}
2 files changed