Record UMA histogram when Form-Not-Secure warning is shown

components/password_manager/core/browser/password_autofill_manager.h

Index: components/password_manager/core/browser/password_autofill_manager.h
diff --git a/components/password_manager/core/browser/password_autofill_manager.h b/components/password_manager/core/browser/password_autofill_manager.h
index 9e3baa58fb76bf47ca7a740431c2356c59b31479..56a5b5c62bac958dfa4b9b903c6aaa05026243d0 100644
--- a/components/password_manager/core/browser/password_autofill_manager.h
+++ b/components/password_manager/core/browser/password_autofill_manager.h
@@ -113,6 +113,10 @@ class PasswordAutofillManager : public autofill::AutofillPopupDelegate {
   // The driver that owns |this|.
   PasswordManagerDriver* password_manager_driver_;
 
+  // True if the Form-Not-Secure warning has been shown on the current
+  // navigation. Used for metrics.
+  bool did_show_form_not_secure_warning_ = false;
+
   autofill::AutofillClient* autofill_client_;  // weak
 
   base::WeakPtrFactory<PasswordAutofillManager> weak_ptr_factory_;