[Offline Pages] Add a GCMAppHandler for offline page prefetch.

components/offline_pages/core/prefetch/prefetch_service_impl.cc

 // Copyright 2017 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 "components/offline_pages/core/prefetch/prefetch_service_impl.h"
+#include "base/memory/ptr_util.h"
 
 namespace offline_pages {
 
-PrefetchServiceImpl::PrefetchServiceImpl() {}
+PrefetchServiceImpl::PrefetchServiceImpl(
+    std::unique_ptr<GCMAppHandler> gcm_app_handler)
+    : gcm_app_handler_(std::move(gcm_app_handler)) {}
 PrefetchServiceImpl::~PrefetchServiceImpl() = default;
 
+void PrefetchServiceImpl::ObserveContentSuggestionsService(
+    ntp_snippets::ContentSuggestionsService* service) {
+  suggested_articles_observer_ =
+      base::MakeUnique<SuggestedArticlesObserver>(service, this);
+}
+
 void PrefetchServiceImpl::AddCandidatePrefetchURLs(
     const std::vector<PrefetchURL>& url_suggestions) {
   NOTIMPLEMENTED();
 }
 void PrefetchServiceImpl::RemoveAllUnprocessedPrefetchURLs(
     const std::string& name_space) {
   NOTIMPLEMENTED();
 }
 
 void PrefetchServiceImpl::RemovePrefetchURLsByClientId(
     const ClientId& client_id) {
   NOTIMPLEMENTED();
 }
 
 void PrefetchServiceImpl::BeginBackgroundTask(
     std::unique_ptr<ScopedBackgroundTask> task) {
   NOTIMPLEMENTED();
 }
 
 void PrefetchServiceImpl::StopBackgroundTask(ScopedBackgroundTask* task) {
   NOTIMPLEMENTED();
 }
 
 void PrefetchServiceImpl::Shutdown() {}
 
 }  // namespace offline_pages