service worker: Clarify comment about when controller endpoint is null.

Change-Id: I2437f4bae9bfd7384d42a586fd7ee6cfba54210d
Reviewed-on: https://chromium-review.googlesource.com/1098418Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#566709}

content/browser/service_worker/service_worker_controllee_request_handler.cc

@@ -258,13 +258,13 @@ ServiceWorkerControlleeRequestHandler::MaybeCreateSubresourceLoaderParams() {
 
   // Otherwise let's send the controller service worker information along
   // with the navigation commit.
-  // Note that |controller_info->endpoint| could be null if the controller
-  // service worker isn't starting up or running, e.g. in no-fetch worker
-  // cases. In that case the renderer frame won't get the controller pointer
-  // upon the navigation commit, and subresource loading will not be intercepted
-  // at least until the frame gets a new controller ptr by SetController.
   SubresourceLoaderParams params;
   auto controller_info = mojom::ControllerServiceWorkerInfo::New();
+  // Note that |controller_info->endpoint| is null if the controller has no
+  // fetch event handler. In that case the renderer frame won't get the
+  // controller pointer upon the navigation commit, and subresource loading will
+  // not be intercepted. (It might get intercepted later if the controller
+  // changes due to skipWaiting() so SetController is sent.)
   controller_info->endpoint =
       provider_host_->GetControllerServiceWorkerPtr().PassInterface();
   controller_info->client_id = provider_host_->client_uuid();

content/common/service_worker/controller_service_worker.mojom

@@ -55,7 +55,7 @@ interface ControllerServiceWorker {
 // commit, and also as a parameter of ServiceWorkerContainer.SetController().
 struct ControllerServiceWorkerInfo {
   // S13nServiceWorker:
-  // Non-null if the controller has fetch event handlers.
+  // Non-null iff the controller has a fetch event handler.
   ControllerServiceWorker? endpoint;
   // S13nServiceWorker:
   // The client being controlled, used for FetchEvent#clientId. The ID is