Update GetClientTag/GetStorageKey comments.

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 440 matching lines @@
     change_processor()->ReportError(
         FROM_HERE, "Failed reading autofill metadata from WebDatabase.");
     return;
   }
   change_processor()->ModelReadyToSync(std::move(batch));
 }
 
 std::string AutocompleteSyncBridge::GetClientTag(
     const EntityData& entity_data) {
   DCHECK(entity_data.specifics.has_autofill());
+  // Must have the format "autofill_entry|$name|$value" where $name and $value
+  // are URL escaped. This is to maintain compatibility with the previous sync
+  // integration (Directory and SyncableService).
   return std::string(kAutocompleteEntryNamespaceTag) +
          EscapeIdentifiers(entity_data.specifics.autofill());
 }
 
 std::string AutocompleteSyncBridge::GetStorageKey(
     const EntityData& entity_data) {
   DCHECK(entity_data.specifics.has_autofill());
+  // Marginally more space efficient than GetClientTag() by omitting the
+  // kAutocompleteEntryNamespaceTag prefix and using protobuf serialization
+  // instead of URL escaping for Unicode characters.
   const AutofillSpecifics specifics = entity_data.specifics.autofill();
   return BuildSerializedStorageKey(specifics.name(), specifics.value());
 }
 
 // AutofillWebDataServiceObserverOnDBThread implementation.
 void AutocompleteSyncBridge::AutofillEntriesChanged(
     const AutofillChangeList& changes) {
   DCHECK(thread_checker_.CalledOnValidThread());
   ActOnLocalChanges(changes);
 }
 
 AutofillTable* AutocompleteSyncBridge::GetAutofillTable() const {
   return AutofillTable::FromWebDatabase(web_data_backend_->GetDatabase());
 }
 
 }  // namespace autofill