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

components/autofill/core/browser/autofill_manager.cc

Index: components/autofill/core/browser/autofill_manager.cc
diff --git a/components/autofill/core/browser/autofill_manager.cc b/components/autofill/core/browser/autofill_manager.cc
index 6c5948a41d01ec5936ac3119a9b09d7401e7d80a..e667d61e77b0877e439fd3c2c534e10e8d2e369a 100644
--- a/components/autofill/core/browser/autofill_manager.cc
+++ b/components/autofill/core/browser/autofill_manager.cc
@@ -1394,6 +1394,9 @@ std::vector<Suggestion> AutofillManager::GetCreditCardSuggestions(
 }
 
 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));