[Most Visited] Check for Sync state when using SuggestionsService.

components/suggestions/suggestions_utils.h

+// Copyright 2014 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_SUGGESTIONS_SUGGESTIONS_UTILS_H_
+#define COMPONENTS_SUGGESTIONS_SUGGESTIONS_UTILS_H_
+
+namespace suggestions {
+
+// Establishes the different sync states that users of SuggestionsService can
+// specify. There are three different concepts in the sync service: initialized,
+// sync enabled and history sync enabled.
+enum SyncState {
+  // State: Sync service is not initialized, yet not disabled. History sync
+  //     state is unknown (since not initialized).
+  // Behavior: Does not issue a server request, but serves from cache if
+  //     available.
+  NOT_INITIALIZED_ENABLED,
+
+  // State: Sync service is initialized, sync is enabled and history sync is
+  //     enabled.
+  // Behavior: Update suggestions from the server. Serve from cache on timeout.
+  INITIALIZED_ENABLED_HISTORY,
+
+  // State: Sync service is disabled or history sync is disabled.
+  // Behavior: Do not issue a server request. Clear the cache. Serve empty
+  //     suggestions.
+  SYNC_OR_HISTORY_SYNC_DISABLED,
+};
+
+// Users of SuggestionsService should always use this function to get SyncState.
+SyncState GetSyncState(bool sync_enabled,
+                       bool sync_initialized,
+                       bool history_sync_enabled);
+
+}  // namespace suggestions
+
+#endif  // COMPONENTS_SUGGESTIONS_SUGGESTIONS_UTILS_H_