Use simpler form of base::DoNothing() where possible.

Change-Id: Ibff3db80b7da087e0ea7870e1ac445bdfd3c81c0
Reviewed-on: https://chromium-review.googlesource.com/967006
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543933}

content/browser/devtools/protocol/service_worker_handler.cc

@@ -213,8 +213,7 @@ Response ServiceWorkerHandler::Unregister(const std::string& scope_url) {
     return CreateDomainNotEnabledErrorResponse();
   if (!context_)
     return CreateContextErrorResponse();
-  context_->UnregisterServiceWorker(GURL(scope_url),
-                                    base::DoNothing::Repeatedly<bool>());
+  context_->UnregisterServiceWorker(GURL(scope_url), base::DoNothing());
   return Response::OK();
 }
 
@@ -223,8 +222,7 @@ Response ServiceWorkerHandler::StartWorker(const std::string& scope_url) {
     return CreateDomainNotEnabledErrorResponse();
   if (!context_)
     return CreateContextErrorResponse();
-  context_->StartServiceWorker(
-      GURL(scope_url), base::DoNothing::Repeatedly<ServiceWorkerStatusCode>());
+  context_->StartServiceWorker(GURL(scope_url), base::DoNothing());
   return Response::OK();
 }