PasswordStore: Clean up expectations about rewriting vectors of forms

chrome/browser/password_manager/password_store_x.cc

Index: chrome/browser/password_manager/password_store_x.cc
diff --git a/chrome/browser/password_manager/password_store_x.cc b/chrome/browser/password_manager/password_store_x.cc
index 71694ad4a5df47528f17f6d728cfffcdff9b8e93..5be5f7f11e87cc58885f3c71114cc67adf71c19d 100644
--- a/chrome/browser/password_manager/password_store_x.cc
+++ b/chrome/browser/password_manager/password_store_x.cc
@@ -146,17 +146,18 @@ ScopedVector<autofill::PasswordForm> PasswordStoreX::FillMatchingLogins(
     // The native backend may succeed and return no data even while locked, if
     // the query did not match anything stored. So we continue to allow fallback
     // until we perform a write operation, or until a read returns actual data.
-    if (matched_forms.size() > 0)
+    if (!matched_forms.empty())
       allow_fallback_ = false;
-  } else if (allow_default_store()) {
-    DCHECK(matched_forms.empty());
-    return PasswordStoreDefault::FillMatchingLogins(form, prompt_policy);
+    return matched_forms.Pass();
   }
-  return matched_forms.Pass();
+  if (allow_default_store())
+    return PasswordStoreDefault::FillMatchingLogins(form, prompt_policy);
+  return ScopedVector<autofill::PasswordForm>();
 }
 
 bool PasswordStoreX::FillAutofillableLogins(
     ScopedVector<autofill::PasswordForm>* forms) {
+  forms->clear();
   CheckMigration();
   if (use_native_backend() && backend_->GetAutofillableLogins(forms)) {
     SortLoginsByOrigin(&forms->get());
@@ -172,6 +173,7 @@ bool PasswordStoreX::FillAutofillableLogins(
 
 bool PasswordStoreX::FillBlacklistLogins(
     ScopedVector<autofill::PasswordForm>* forms) {
+  forms->clear();
   CheckMigration();
   if (use_native_backend() && backend_->GetBlacklistLogins(forms)) {
     // See GetLoginsImpl() for why we disallow fallback conditionally here.
@@ -221,8 +223,12 @@ bool PasswordStoreX::allow_default_store() {
 ssize_t PasswordStoreX::MigrateLogins() {
   DCHECK(backend_.get());
   ScopedVector<autofill::PasswordForm> forms;
+  ScopedVector<autofill::PasswordForm> blacklist_forms;
   bool ok = PasswordStoreDefault::FillAutofillableLogins(&forms) &&
-      PasswordStoreDefault::FillBlacklistLogins(&forms);
+            PasswordStoreDefault::FillBlacklistLogins(&blacklist_forms);
+  forms.reserve(forms.size() + blacklist_forms.size());
+  forms.insert(forms.end(), blacklist_forms.begin(), blacklist_forms.end());
+  blacklist_forms.weak_clear();
   if (ok) {
     // We add all the passwords (and blacklist entries) to the native backend
     // before attempting to remove any from the login database, to make sure we