[USS] Implement GetAllData and GetStorageKey.

components/history/core/browser/history_backend.h

 // Copyright (c) 2012 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_HISTORY_CORE_BROWSER_HISTORY_BACKEND_H_
 #define COMPONENTS_HISTORY_CORE_BROWSER_HISTORY_BACKEND_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 560 matching lines @@
   FRIEND_TEST_ALL_PREFIXES(HistoryBackendTest, TopHosts_IgnoreUnusualURLs);
   FRIEND_TEST_ALL_PREFIXES(HistoryBackendTest, HostRankIfAvailable);
   FRIEND_TEST_ALL_PREFIXES(HistoryBackendTest, RecordTopHostsMetrics);
   FRIEND_TEST_ALL_PREFIXES(HistoryBackendTest, GetCountsAndLastVisitForOrigins);
   FRIEND_TEST_ALL_PREFIXES(HistoryBackendTest, UpdateVisitDuration);
   FRIEND_TEST_ALL_PREFIXES(HistoryBackendTest, ExpireHistoryForTimes);
   FRIEND_TEST_ALL_PREFIXES(HistoryBackendTest, DeleteFTSIndexDatabases);
   FRIEND_TEST_ALL_PREFIXES(ProfileSyncServiceTypedUrlTest,
                            ProcessUserChangeRemove);
   friend class ::TestingProfile;
+  friend class TypedURLSyncBridgeTest;

[pavely, 2017/05/30 14:25:40]

I assume you make TypedURLSyncBridgeTest a friend just to give it ability to
inject typed_url_sync_bridge_.
Written this way it allows TypedURLSyncBridgeTest to call any private method and
modify any private field of HistoryBackend. This makes it hard to form an
expectation of the kinds of modifications test actually does.
I think it is better to create public helper function for test that allows to
inject typed_url_sync_bridge_. This way it is clear that test doesn't have any
special privileges  with HistoryBackend.

[Gang Wu, 2017/05/31 00:17:32]

Done.

 
   // Returns the name of the Favicons database. This is the new name
   // of the Thumbnails database.
   base::FilePath GetFaviconsFileName() const;
 
   class URLQuerier;
   friend class URLQuerier;
 
   // Does the work of Init.
   void InitImpl(const HistoryDatabaseParams& history_database_params);
@@ skipping 324 matching lines @@
   // it unregisters itself as observer during destruction.
   std::unique_ptr<TypedUrlSyncableService> typed_url_syncable_service_;
   std::unique_ptr<TypedURLSyncBridge> typed_url_sync_bridge_;
 
   DISALLOW_COPY_AND_ASSIGN(HistoryBackend);
 };
 
 }  // namespace history
 
 #endif  // COMPONENTS_HISTORY_CORE_BROWSER_HISTORY_BACKEND_H_