[USS] Implement GetAllData and GetStorageKey.

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 59eb0756af96e44b24388505a3ba8d080c8257ad..c50f8a67d65b24577631edcd45e715d30cb819a6 100644
--- a/components/history/core/browser/typed_url_sync_bridge.h
+++ b/components/history/core/browser/typed_url_sync_bridge.h
@@ -5,15 +5,13 @@
 #ifndef COMPONENTS_HISTORY_CORE_BROWSER_TYPED_URL_SYNC_BRIDGE_H_
 #define COMPONENTS_HISTORY_CORE_BROWSER_TYPED_URL_SYNC_BRIDGE_H_
 
+#include "base/scoped_observer.h"
 #include "components/history/core/browser/history_backend_observer.h"
+#include "components/history/core/browser/typed_url_sync_metadata_database.h"
 #include "components/sync/model/metadata_change_list.h"
 #include "components/sync/model/model_type_sync_bridge.h"
 #include "components/sync/model/sync_error.h"
 
-namespace syncer {
-class SyncMetadataStore;
-}
-
 namespace history {
 
 class TypedURLSyncBridge : public syncer::ModelTypeSyncBridge,
@@ -22,7 +20,7 @@ class TypedURLSyncBridge : public syncer::ModelTypeSyncBridge,
   // |sync_metadata_store| is owned by |history_backend|, and must outlive
   // TypedURLSyncBridge.
   TypedURLSyncBridge(HistoryBackend* history_backend,
-                     syncer::SyncMetadataStore* sync_metadata_store,
+                     TypedURLSyncMetadataDatabase* sync_metadata_store,
                      const ChangeProcessorFactory& change_processor_factory);
   ~TypedURLSyncBridge() override;
 
@@ -54,19 +52,65 @@ class TypedURLSyncBridge : public syncer::ModelTypeSyncBridge,
                      const history::URLRows& deleted_rows,
                      const std::set<GURL>& favicon_urls) override;
 
+  // Returns the percentage of DB accesses that have resulted in an error.
+  int GetErrorPercentage() const;
+
+  // Return true if this function successfully converts the passed URL
+  // information to a TypedUrlSpecifics structure for writing to the sync DB.
+  static bool WriteToTypedUrlSpecifics(const URLRow& url,
+                                       const VisitVector& visits,
+                                       sync_pb::TypedUrlSpecifics* specifics)
+      WARN_UNUSED_RESULT;
+
  private:
+  friend class TypedURLSyncBridgeTest;
+
+  // Synchronously load sync metadata from the TypedURLSyncMetadataDatabase and
+  // pass it to the processor so that it can start tracking changes.
+  void LoadMetadata();
+
+  // Helper function that clears our error counters (used to reset stats after
+  // merge so we can track merge errors separately).
+  void ClearErrorStats();
+
+  // 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
+  // last_visit timestamp, huge data sets that exhaust memory when fetched,
+  // expired visits that are not deleted by |ExpireHistoryBackend|, etc) by
+  // modifying the passed |url| object and |visits| vector.

[brettw, 2017/06/05 17:31:15]

Can this document the ordering of the resulting visits vector?

[Gang Wu, 2017/06/05 20:04:14]

Done.

+  // Returns false in two cases.
+  // 1. we could not fetch the visits for the passed URL, DB error.
+  // 2. No visits for the passed url, or all the visits are expired.
+  bool FixupURLAndGetVisits(URLRow* url, VisitVector* visits);
+
+  // Create an EntityData by URL |row| and its visits |visits|.
+  std::unique_ptr<syncer::EntityData> CreateEntityData(
+      const URLRow& row,
+      const VisitVector& visits);
+
   // A non-owning pointer to the backend, which we're syncing local changes from
   // and sync changes to.
   HistoryBackend* const history_backend_;
 
   // A non-owning pointer to the database, which is for storing typed urls sync
   // metadata and state.
-  syncer::SyncMetadataStore* const sync_metadata_store_;
+  TypedURLSyncMetadataDatabase* const sync_metadata_database_;
+
+  // Statistics for the purposes of tracking the percentage of DB accesses that
+  // fail for each client via UMA.
+  int num_db_accesses_;
+  int num_db_errors_;
 
   // Since HistoryBackend use SequencedTaskRunner, so should use SequenceChecker
   // here.
   base::SequenceChecker sequence_checker_;
 
+  // Tracks observed history backend, for receiving updates from history
+  // backend.
+  ScopedObserver<history::HistoryBackend, history::HistoryBackendObserver>
+      history_backend_observer_;
+
   DISALLOW_COPY_AND_ASSIGN(TypedURLSyncBridge);
 };