service worker: Clarify the navigation preload network error message.

content/renderer/service_worker/service_worker_context_client.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/renderer/service_worker/service_worker_context_client.h"
 
 #include <memory>
 #include <utility>
 
 #include "base/lazy_instance.h"
@@ skipping 406 matching lines @@
 
   void OnStartLoadingResponseBody(
       mojo::ScopedDataPipeConsumerHandle body) override {
     DCHECK(!body_.is_valid());
     body_ = std::move(body);
     MaybeReportResponseToClient();
   }
 
   void OnComplete(const ResourceRequestCompletionStatus& status) override {
     if (status.error_code != net::OK) {
+      std::string error_message;
+      if (status.error_code == net::ERR_ABORTED) {
+        error_message =
+            "The service worker navigation preload request was cancelled "
+            "before 'preloadResponse' settled. If you intend to use "
+            "'preloadResponse', use waitUntil() or respondWith() to wait for "
+            "the promise to settle.";
+      } else {
+        error_message = base::StringPrintf(
+            "The service worker navigation preload request failed with network "
+            "error code %d.",
+            status.error_code);

[horo, 2017/04/12 00:32:03]

I think we should not expose the error code for security and privacy reason.
Is there any other JS API which expose the network error code?

+      }
       // This will delete |this|.
-      ReportErrorToClient("Service Worker navigation preload network error.");
+      ReportErrorToClient(error_message);
       return;
     }
 
     ServiceWorkerContextClient* client =
         ServiceWorkerContextClient::ThreadSpecificInstance();
     if (!client)
       return;
     if (response_) {
       // When the response body from the server is empty, OnComplete() is called
       // without OnStartLoadingResponseBody().
@@ skipping 12 matching lines @@
     ServiceWorkerContextClient* client =
         ServiceWorkerContextClient::ThreadSpecificInstance();
     if (!client)
       return;
 
     client->OnNavigationPreloadResponse(
         fetch_event_id_, std::move(response_),
         base::MakeUnique<WebDataConsumerHandleImpl>(std::move(body_)));
   }
 
-  void ReportErrorToClient(const char* error_message) {
+  void ReportErrorToClient(const std::string& error_message) {
     ServiceWorkerContextClient* client =
         ServiceWorkerContextClient::ThreadSpecificInstance();
     if (!client)
       return;
     // This will delete |this|.
     client->OnNavigationPreloadError(
         fetch_event_id_, base::MakeUnique<blink::WebServiceWorkerError>(
                              blink::WebServiceWorkerError::kErrorTypeNetwork,
                              blink::WebString::FromUTF8(error_message)));
   }
@@ skipping 1049 matching lines @@
 }
 
 base::WeakPtr<ServiceWorkerContextClient>
 ServiceWorkerContextClient::GetWeakPtr() {
   DCHECK(worker_task_runner_->RunsTasksOnCurrentThread());
   DCHECK(context_);
   return context_->weak_factory.GetWeakPtr();
 }
 
 }  // namespace content