service worker: Remove unused implementation of a virtual function.

All subclasses define their own RequestStillValid() already, so we can
make it a pure virtual method.

Change-Id: Ic5bf5deb40eb52e6f93733a5770b1e3f1761b91f
Reviewed-on: https://chromium-review.googlesource.com/c/1317418Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Commit-Queue: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605255}

content/browser/service_worker/service_worker_url_job_wrapper.h

@@ -46,7 +46,7 @@ class CONTENT_EXPORT ServiceWorkerURLJobWrapper {
     // the request should still continue, or if processing should be aborted.
     // When false is returned, this sets |*result| to an appropriate error.
     virtual bool RequestStillValid(
-        ServiceWorkerMetrics::URLRequestJobResult* result);
+        ServiceWorkerMetrics::URLRequestJobResult* result) = 0;
 
     // Called to signal that loading failed, and that the resource being loaded
     // was a main resource.

content/browser/service_worker/service_worker_url_request_job.cc

@@ -304,11 +304,6 @@ class ServiceWorkerURLRequestJob::NavigationPreloadMetrics {
   DISALLOW_COPY_AND_ASSIGN(NavigationPreloadMetrics);
 };
 
-bool ServiceWorkerURLRequestJob::Delegate::RequestStillValid(
-    ServiceWorkerMetrics::URLRequestJobResult* result) {
-  return true;
-}
-
 ServiceWorkerURLRequestJob::ServiceWorkerURLRequestJob(
     net::URLRequest* request,
     net::NetworkDelegate* network_delegate,