[USS] Implement ApplySyncChanges and OnURLVisited/Modified/Deleted.

components/history/core/browser/typed_url_sync_bridge.h

Index: components/history/core/browser/typed_url_sync_bridge.h
diff --git a/components/history/core/browser/typed_url_sync_bridge.h b/components/history/core/browser/typed_url_sync_bridge.h
index 13a8bbd9bc542c06a0f4c68fa0f0dca6485f5844..2d836c87b114c091e8c07facce7c63534aa7416f 100644
--- a/components/history/core/browser/typed_url_sync_bridge.h
+++ b/components/history/core/browser/typed_url_sync_bridge.h
@@ -102,6 +102,16 @@ class TypedURLSyncBridge : public syncer::ModelTypeSyncBridge,
                                history::URLRow* new_url,
                                std::vector<history::VisitInfo>* new_visits);
 
+  // Diffs the set of visits between the history DB and the sync DB, using the
+  // sync DB as the canonical copy. Result is the set of |new_visits| and
+  // |removed_visits| that can be applied to the history DB to make it match
+  // the sync DB version. |removed_visits| can be null if the caller does not
+  // care about which visits to remove.
+  static void DiffVisits(const history::VisitVector& history_visits,
+                         const sync_pb::TypedUrlSpecifics& sync_specifics,
+                         std::vector<history::VisitInfo>* new_visits,
+                         history::VisitVector* removed_visits);
+
   // Fills |new_url| with formatted data from |typed_url|.
   static void UpdateURLRowFromTypedUrlSpecifics(
       const sync_pb::TypedUrlSpecifics& typed_url,
@@ -118,12 +128,31 @@ class TypedURLSyncBridge : public syncer::ModelTypeSyncBridge,
   // Compares |server_typed_url| from the server against local history to decide
   // how to merge any existing data, and updates appropriate data containers to
   // write to server and backend.
-  void UpdateUrlFromServer(const sync_pb::TypedUrlSpecifics& server_typed_url,
-                           TypedURLMap* local_typed_urls,
-                           URLVisitVectorMap* visit_vectors,
-                           history::URLRows* new_synced_urls,
-                           TypedURLVisitVector* new_synced_visits,
-                           history::URLRows* updated_synced_urls);
+  void MergeURLWithSync(const sync_pb::TypedUrlSpecifics& server_typed_url,
+                        TypedURLMap* local_typed_urls,
+                        URLVisitVectorMap* visit_vectors,
+                        history::URLRows* new_synced_urls,
+                        TypedURLVisitVector* new_synced_visits,
+                        history::URLRows* updated_synced_urls);
+
+  // Given a typed URL in the sync DB, looks for an existing entry in the
+  // local history DB and generates a list of visits to add to the
+  // history DB to bring it up to date (avoiding duplicates).
+  // Updates the passed |visits_to_add| and |visits_to_remove| vectors with the
+  // visits to add to/remove from the history DB, and adds a new entry to either
+  // |updated_urls| or |new_urls| depending on whether the URL already existed
+  // in the history DB.
+  void UpdateFromSync(const sync_pb::TypedUrlSpecifics& typed_url,
+                      TypedURLVisitVector* visits_to_add,
+                      history::VisitVector* visits_to_remove,
+                      history::URLRows* updated_urls,
+                      history::URLRows* new_urls);
+
+  // Utility routine that either updates an existing sync node or creates a
+  // new one for the passed |typed_url| if one does not already exist. Returns
+  // false and sets an unrecoverable error if the operation failed.

[pavely, 2017/07/06 19:28:29]

I don't think it sets unrecoverable error anymore.

[Gang Wu, 2017/07/10 19:53:25]

Done.

+  bool UpdateSyncFromLocal(URLRow typed_url,
+                           syncer::MetadataChangeList* metadata_change_list);

[pavely, 2017/07/06 19:28:29]

I don't think callers check return value of this function. Should they? Or
should this function return void?

[Gang Wu, 2017/07/10 19:53:25]

Done.

 
   // Writes new typed url data from sync server to history backend.
   base::Optional<syncer::ModelError> WriteToHistoryBackend(
@@ -147,6 +176,12 @@ class TypedURLSyncBridge : public syncer::ModelTypeSyncBridge,
   // of sync, based on the visits the URL had.
   bool ShouldIgnoreVisits(const history::VisitVector& visits);
 
+  // Returns true if the caller should sync as a result of the passed visit
+  // notification. We use this to throttle the number of sync changes we send
+  // to the server so we don't hit the server for every
+  // single typed URL visit.
+  bool ShouldSyncVisit(int typed_count, ui::PageTransition transition);
+
   // Fetches visits from the history DB corresponding to the passed URL. This
   // function compensates for the fact that the history DB has rather poor data
   // integrity (duplicate visits, visit timestamps that don't match the