[USS] Implement GetAllData and GetStorageKey.

components/history/core/browser/history_backend.h

Index: components/history/core/browser/history_backend.h
diff --git a/components/history/core/browser/history_backend.h b/components/history/core/browser/history_backend.h
index 59c58389c1294a9e956c3e76b35e0a53240313c8..fd1faccc2f7627269a4c8e0a97f172be156755b7 100644
--- a/components/history/core/browser/history_backend.h
+++ b/components/history/core/browser/history_backend.h
@@ -578,6 +578,7 @@ class HistoryBackend : public base::RefCountedThreadSafe<HistoryBackend>,
   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.