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

sync/syncable/deferred_on_disk_directory_backing_store_unittest.cc

 // Copyright 2014 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.
 
 #include "base/files/scoped_temp_dir.h"
 #include "base/stl_util.h"
 #include "sync/syncable/deferred_on_disk_directory_backing_store.h"
 #include "sync/syncable/directory.h"
 #include "sync/syncable/entry_kernel.h"
 #include "sync/syncable/on_disk_directory_backing_store.h"
@@ skipping 13 matching lines @@
     CHECK(temp_dir_.CreateUniqueTempDir());
     db_path_ = temp_dir_.path().Append(kSyncDataFolderName);
   }
 
   void TearDown() override { STLDeleteValues(&handles_map_); }
 
   base::ScopedTempDir temp_dir_;
   base::FilePath db_path_;
   Directory::MetahandlesMap handles_map_;
   JournalIndex delete_journals_;
+  MetahandleSet metahandles_to_purge_;
   Directory::KernelLoadInfo kernel_load_info_;
 };
 
 // Test initialization of root entry when calling Load().
 TEST_F(DeferredOnDiskDirectoryBackingStoreTest, Load) {
   DeferredOnDiskDirectoryBackingStore store("test", db_path_);
   EXPECT_EQ(OPENED, store.Load(&handles_map_, &delete_journals_,
-                               &kernel_load_info_));
+                               &metahandles_to_purge_, &kernel_load_info_));
   EXPECT_TRUE(delete_journals_.empty());
+  EXPECT_TRUE(metahandles_to_purge_.empty());
   ASSERT_EQ(1u, handles_map_.size());   // root node
   ASSERT_TRUE(handles_map_.count(1));
   EntryKernel* root = handles_map_[1];
   EXPECT_TRUE(root->ref(ID).IsRoot());
   EXPECT_EQ(1, root->ref(META_HANDLE));
   EXPECT_TRUE(root->ref(IS_DIR));
 }
 
 // Test on-disk DB is not created if SaveChanges() is not called.
 TEST_F(DeferredOnDiskDirectoryBackingStoreTest,
        DontPersistIfSavingChangesNotCalled) {
   {
     // Open and close.
     DeferredOnDiskDirectoryBackingStore store("test", db_path_);
     EXPECT_EQ(OPENED, store.Load(&handles_map_, &delete_journals_,
-                                 &kernel_load_info_));
+                                 &metahandles_to_purge_, &kernel_load_info_));
   }
 
   EXPECT_FALSE(base::PathExists(db_path_));
 }
 
 // Test on-disk DB is not created when there are no changes.
 TEST_F(DeferredOnDiskDirectoryBackingStoreTest,
        DontPersistWhenSavingNoChanges) {
   {
     // Open and close.
     DeferredOnDiskDirectoryBackingStore store("test", db_path_);
     EXPECT_EQ(OPENED, store.Load(&handles_map_, &delete_journals_,
-                                 &kernel_load_info_));
+                                 &metahandles_to_purge_, &kernel_load_info_));
 
     Directory::SaveChangesSnapshot snapshot;
     store.SaveChanges(snapshot);
   }
 
   EXPECT_FALSE(base::PathExists(db_path_));
 }
 
 // Test changes are persisted to disk when SaveChanges() is called.
 TEST_F(DeferredOnDiskDirectoryBackingStoreTest, PersistWhenSavingValidChanges) {
   {
     // Open and close.
     DeferredOnDiskDirectoryBackingStore store("test", db_path_);
     EXPECT_EQ(OPENED, store.Load(&handles_map_, &delete_journals_,
-                                 &kernel_load_info_));
+                                 &metahandles_to_purge_, &kernel_load_info_));
 
     Directory::SaveChangesSnapshot snapshot;
     EntryKernel* entry = new EntryKernel();
     entry->put(ID, Id::CreateFromClientString("test_entry"));
     entry->put(META_HANDLE, 2);
     entry->mark_dirty(NULL);
     snapshot.dirty_metas.insert(entry);
     store.SaveChanges(snapshot);
   }
 
   STLDeleteValues(&handles_map_);
 
   ASSERT_TRUE(base::PathExists(db_path_));
   OnDiskDirectoryBackingStore read_store("test", db_path_);
-  EXPECT_EQ(OPENED, read_store.Load(&handles_map_, &delete_journals_,
-                                    &kernel_load_info_));
+  EXPECT_EQ(OPENED,
+            read_store.Load(&handles_map_, &delete_journals_,
+                            &metahandles_to_purge_, &kernel_load_info_));
   ASSERT_EQ(2u, handles_map_.size());
   ASSERT_TRUE(handles_map_.count(1));     // root node
   ASSERT_TRUE(handles_map_.count(2));
   EntryKernel* entry = handles_map_[2];
   EXPECT_EQ(Id::CreateFromClientString("test_entry"), entry->ref(ID));
 }
 
 }  // namespace
 }  // namespace syncable
 }  // namespace syncer