Sync: Avoid 3 passes over SyncDarta DB when loading the directory from the disk

sync/syncable/on_disk_directory_backing_store.h

 // Copyright 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 SYNC_SYNCABLE_ON_DISK_DIRECTORY_BACKING_STORE_H_
 #define SYNC_SYNCABLE_ON_DISK_DIRECTORY_BACKING_STORE_H_
 
 #include "base/files/file_path.h"
 #include "sync/base/sync_export.h"
 #include "sync/syncable/directory_backing_store.h"
 
 namespace syncer {
 namespace syncable {
 
 // This is the concrete class that provides a useful implementation of
 // DirectoryBackingStore.
 class SYNC_EXPORT_PRIVATE OnDiskDirectoryBackingStore
     : public DirectoryBackingStore {
  public:
   OnDiskDirectoryBackingStore(const std::string& dir_name,
                               const base::FilePath& backing_filepath);
   ~OnDiskDirectoryBackingStore() override;
   DirOpenResult Load(Directory::MetahandlesMap* handles_map,
                      JournalIndex* delete_journals,
+                     MetahandleSet* metahandles_to_purge,
                      Directory::KernelLoadInfo* kernel_load_info) override;
 
   // A helper function that will make one attempt to load the directory.
   // Unlike Load(), it does not attempt to recover from failure.
-  DirOpenResult TryLoad(
-      Directory::MetahandlesMap* handles_map,
-      JournalIndex* delete_journals,
-      Directory::KernelLoadInfo* kernel_load_info);
+  DirOpenResult TryLoad(Directory::MetahandlesMap* handles_map,
+                        JournalIndex* delete_journals,
+                        MetahandleSet* metahandles_to_purge,
+                        Directory::KernelLoadInfo* kernel_load_info);
 
  protected:
   // Subclasses may override this to avoid a possible DCHECK.
   virtual void ReportFirstTryOpenFailure();
 
  private:
   FRIEND_TEST_ALL_PREFIXES(DirectoryBackingStoreTest, MinorCorruption);
 
   bool allow_failure_for_test_;
   base::FilePath backing_filepath_;
 
   DISALLOW_COPY_AND_ASSIGN(OnDiskDirectoryBackingStore);
 };
 
 }  // namespace syncable
 }  // namespace syncer
 
 #endif  // SYNC_SYNCABLE_ON_DISK_DIRECTORY_BACKING_STORE_H_