[sync] Check against nullptr web_data_backend->GetDatabase()

components/autofill/core/browser/webdata/autocomplete_sync_bridge.cc

 // Copyright 2016 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/autofill/core/browser/webdata/autocomplete_sync_bridge.h"
 
 #include <algorithm>
 #include <set>
 #include <unordered_set>
 #include <utility>
@@ skipping 430 matching lines @@
         break;
       }
     }
   }
 
   if (Optional<ModelError> error = metadata_change_list->TakeError())
     change_processor()->ReportError(error.value());
 }
 
 void AutocompleteSyncBridge::LoadMetadata() {
+  if (!web_data_backend_ || !web_data_backend_->GetDatabase() ||
+      !GetAutofillTable()) {
+    change_processor()->ReportError(FROM_HERE,
+                                    "Failed to load AutofillWebDatabase.");
+    return;
+  }
+
   auto batch = base::MakeUnique<syncer::MetadataBatch>();
   if (!GetAutofillTable()->GetAllSyncMetadata(syncer::AUTOFILL, batch.get())) {
     change_processor()->ReportError(
         FROM_HERE, "Failed reading autofill metadata from WebDatabase.");
     return;
   }
   change_processor()->ModelReadyToSync(std::move(batch));
 }
 
 std::string AutocompleteSyncBridge::GetClientTag(
@@ skipping 21 matching lines @@
     const AutofillChangeList& changes) {
   DCHECK(thread_checker_.CalledOnValidThread());
   ActOnLocalChanges(changes);
 }
 
 AutofillTable* AutocompleteSyncBridge::GetAutofillTable() const {
   return AutofillTable::FromWebDatabase(web_data_backend_->GetDatabase());
 }
 
 }  // namespace autofill