[sync] Verify existence of the root when loading DirectoryBackingStore

components/sync/syncable/directory_backing_store.cc

 // 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.
 
 #include "components/sync/syncable/directory_backing_store.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <limits>
@@ skipping 1624 matching lines @@
       "store_birthday TEXT, "
       "db_create_version TEXT, "
       "db_create_time INT, "
       "next_id INT default -2, "
       "cache_guid TEXT )");
   return db_->Execute(query.c_str());
 }
 
 // This function checks to see if the given list of Metahandles has any nodes
 // whose PARENT_ID values refer to ID values that do not actually exist.
+// This function also checks that the root node exists in the set.

[pavely, 2016/09/15 22:50:15]

I would say "that root node with correct id exists...".

 // Returns true on success.
 bool DirectoryBackingStore::VerifyReferenceIntegrity(
     const Directory::MetahandlesMap* handles_map) {
   TRACE_EVENT0("sync", "SyncDatabaseIntegrityCheck");
   typedef std::unordered_set<std::string> IdsSet;
 
   IdsSet ids_set;
   bool is_ok = true;
 
   for (auto it = handles_map->begin(); it != handles_map->end(); ++it) {
     EntryKernel* entry = it->second.get();
     bool is_duplicate_id = !(ids_set.insert(entry->ref(ID).value()).second);
     is_ok = is_ok && !is_duplicate_id;
   }
 
   IdsSet::iterator end = ids_set.end();
   for (auto it = handles_map->begin(); it != handles_map->end(); ++it) {
     EntryKernel* entry = it->second.get();
     if (!entry->ref(PARENT_ID).IsNull()) {
       bool parent_exists = (ids_set.find(entry->ref(PARENT_ID).value()) != end);
       if (!parent_exists) {
         return false;
       }
     }
   }
+  if (ids_set.find(Id::GetRoot().value()) == ids_set.end()) {

[pavely, 2016/09/15 22:50:15]

nit: Since you are using Id class directly could you include syncable_id.h

+    return false;
+  }
   return is_ok;
 }
 
 void DirectoryBackingStore::PrepareSaveEntryStatement(
     EntryTable table, sql::Statement* save_statement) {
   if (save_statement->is_valid())
     return;
 
   string query;
   query.reserve(kUpdateStatementBufferSize);
@@ skipping 79 matching lines @@
   DCHECK(CalledOnValidThread());
   DCHECK(!catastrophic_error_handler.is_null());
   catastrophic_error_handler_ = catastrophic_error_handler;
   sql::Connection::ErrorCallback error_callback =
       base::Bind(&OnSqliteError, catastrophic_error_handler_);
   db_->set_error_callback(error_callback);
 }
 
 }  // namespace syncable
 }  // namespace syncer