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

components/offline_pages/core/prefetch/prefetch_gcm_handler.h

+// 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.
+
+#ifndef COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_GCM_HANDLER_H_
+#define COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_GCM_HANDLER_H_
+
+#include <string>
+
+namespace gcm {
+class GCMAppHandler;
+}  // namespace gcm
+
+namespace offline_pages {
+
+class PrefetchGCMHandler;
+
+// Main class and entry point for the Offline Pages Prefetching feature, that
+// controls the lifetime of all major subcomponents of the prefetching system.
+class PrefetchGCMHandler {
+ public:
+  virtual ~PrefetchGCMHandler() = default;
+
+  // Returns the GCMAppHandler for this object.  Can return |nullptr| in unit
+  // tests.
+  virtual gcm::GCMAppHandler* AsGCMAppHandler() = 0;
+
+  // The app ID to register with at the GCM layer.
+  virtual std::string GetAppId() const = 0;
+
+  // TODO(dewittj): Add methods for acquiring an Instance ID token to this
+  // interface.
+};
+
+}  // namespace offline_pages
+
+#endif  // COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_GCM_HANDLER_H_