[Autofill] Return early when no new forms are parsed.

components/autofill/core/browser/autofill_manager.cc

 // Copyright 2013 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/autofill_manager.h"
 
 #include <stddef.h>
 
 #include <limits>
 #include <map>
@@ skipping 1376 matching lines @@
   std::vector<Suggestion> suggestions =
       personal_data_->GetCreditCardSuggestions(type, field.value);
   for (size_t i = 0; i < suggestions.size(); i++) {
     suggestions[i].frontend_id =
         MakeFrontendID(suggestions[i].backend_id, std::string());
   }
   return suggestions;
 }
 
 void AutofillManager::ParseForms(const std::vector<FormData>& forms) {
+  if (forms.empty())
+    return;
+
   std::vector<FormStructure*> non_queryable_forms;
   for (const FormData& form : forms) {
     scoped_ptr<FormStructure> form_structure(new FormStructure(form));
 
     if (!form_structure->ShouldBeParsed()) {
       if (form_structure->has_password_field()) {
         AutofillMetrics::LogPasswordFormQueryVolume(
             AutofillMetrics::NEW_PASSWORD_QUERY);
       }
       continue;
@@ skipping 150 matching lines @@
     if (i > 0)
       fputs("Next oldest form:\n", file);
   }
   fputs("\n", file);
 
   fclose(file);
 }
 #endif  // ENABLE_FORM_DEBUG_DUMP
 
 }  // namespace autofill