Autofill: Set requirements for number of recognized fields in an autofillable form

components/autofill/content/renderer/form_cache.h

Index: components/autofill/content/renderer/form_cache.h
diff --git a/components/autofill/content/renderer/form_cache.h b/components/autofill/content/renderer/form_cache.h
index d0c29cdaf8114a245a829d7b05dfa165be1e6c7c..bcc318b104c238980f008a0e54be07800e4493a0 100644
--- a/components/autofill/content/renderer/form_cache.h
+++ b/components/autofill/content/renderer/form_cache.h
@@ -34,7 +34,9 @@ class FormCache {
 
   // Scans the DOM in |frame_| extracting and storing forms that have not been
   // seen before. Returns the extracted forms.
-  std::vector<FormData> ExtractNewForms();
+  // Writes the index of the unowned form to |unowned_form_index|, or the size
+  // of the returned vector if no unowned form exists.
+  std::vector<FormData> ExtractNewForms(size_t* unowned_form_index);
 
   // Resets the forms.
   void Reset();