PasswordStore: Clean up expectations about rewriting vectors of forms

components/password_manager/core/browser/password_store_default.cc

Index: components/password_manager/core/browser/password_store_default.cc
diff --git a/components/password_manager/core/browser/password_store_default.cc b/components/password_manager/core/browser/password_store_default.cc
index 88f6e9e45fe47f83a99df12fad70d62a5dd9e340..51ab57efe17dc5f9f61bc87cf5ade70cc9ee7780 100644
--- a/components/password_manager/core/browser/password_store_default.cc
+++ b/components/password_manager/core/browser/password_store_default.cc
@@ -115,8 +115,8 @@ ScopedVector<autofill::PasswordForm> PasswordStoreDefault::FillMatchingLogins(
     const autofill::PasswordForm& form,
     AuthorizationPromptPolicy prompt_policy) {
   ScopedVector<autofill::PasswordForm> matched_forms;
-  if (login_db_)
-    login_db_->GetLogins(form, &matched_forms);
+  if (login_db_ && !login_db_->GetLogins(form, &matched_forms))
+    matched_forms.clear();
   return matched_forms.Pass();
 }
 
@@ -137,12 +137,14 @@ void PasswordStoreDefault::GetBlacklistLoginsImpl(
 bool PasswordStoreDefault::FillAutofillableLogins(
     ScopedVector<autofill::PasswordForm>* forms) {
   DCHECK(GetBackgroundTaskRunner()->BelongsToCurrentThread());
+  forms->clear();
   return login_db_ && login_db_->GetAutofillableLogins(forms);
 }
 
 bool PasswordStoreDefault::FillBlacklistLogins(
     ScopedVector<autofill::PasswordForm>* forms) {
   DCHECK(GetBackgroundTaskRunner()->BelongsToCurrentThread());
+  forms->clear();
   return login_db_ && login_db_->GetBlacklistLogins(forms);
 }