[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 <utility>
 
 #include "base/memory/ptr_util.h"
 #include "components/offline_pages/core/prefetch/prefetch_dispatcher_impl.h"
 
 namespace offline_pages {
 
-PrefetchServiceImpl::PrefetchServiceImpl()
-    : dispatcher_(base::MakeUnique<PrefetchDispatcherImpl>()) {}
+PrefetchServiceImpl::PrefetchServiceImpl(
+    std::unique_ptr<PrefetchGCMHandler> gcm_handler)
+    : gcm_handler_(std::move(gcm_handler)),
+      dispatcher_(base::MakeUnique<PrefetchDispatcherImpl>()) {}
 
 PrefetchServiceImpl::~PrefetchServiceImpl() = default;
 
+PrefetchGCMHandler* PrefetchServiceImpl::GetPrefetchGCMHandler() {
+  return gcm_handler_.get();
+}
+
 PrefetchDispatcher* PrefetchServiceImpl::GetDispatcher() {
   return dispatcher_.get();
-};
+}
+
+void PrefetchServiceImpl::ObserveContentSuggestionsService(
+    ntp_snippets::ContentSuggestionsService* service) {
+  suggested_articles_observer_ =
+      base::MakeUnique<SuggestedArticlesObserver>(service, this);
+}
 
 void PrefetchServiceImpl::Shutdown() {}
 
 }  // namespace offline_pages