PasswordStore: Clean up expectations about rewriting vectors of forms

components/password_manager/core/browser/password_syncable_service.cc

Index: components/password_manager/core/browser/password_syncable_service.cc
diff --git a/components/password_manager/core/browser/password_syncable_service.cc b/components/password_manager/core/browser/password_syncable_service.cc
index b036b50605ed882a757f1d4f770b66656d3681b0..870aecbbfd453f65e0477fbaedd9aa2bd34644c4 100644
--- a/components/password_manager/core/browser/password_syncable_service.cc
+++ b/components/password_manager/core/browser/password_syncable_service.cc
@@ -303,8 +303,9 @@ bool PasswordSyncableService::ReadFromPasswordStore(
     ScopedVector<autofill::PasswordForm>* password_entries,
     PasswordEntryMap* passwords_entry_map) const {
   DCHECK(password_entries);
+  ScopedVector<autofill::PasswordForm> blacklist_entries;
   if (!password_store_->FillAutofillableLogins(password_entries) ||
-      !password_store_->FillBlacklistLogins(password_entries)) {
+      !password_store_->FillBlacklistLogins(&blacklist_entries)) {
     // Password store often fails to load passwords. Track failures with UMA.
     // (http://crbug.com/249000)
     UMA_HISTOGRAM_ENUMERATION("Sync.LocalDataFailedToLoad",
@@ -312,6 +313,12 @@ bool PasswordSyncableService::ReadFromPasswordStore(
                               syncer::MODEL_TYPE_COUNT);
     return false;
   }
+  // Move |blacklist_entries| to |password_entries|.
+  password_entries->reserve(password_entries->size() +

[engedy, 2015/03/09 13:33:18]

Is this necessary?

[vabr (Chromium), 2015/03/09 17:44:15]

Ideally, insert() would do resize when called on a range, but I have not found
any documented guarantee for that.

Performance-wise the necessity is also not clear, given that the typical sizes
of the vectors are not clear to me.

But reserve() is used in the codebase well enough to keep this code reasonably
readable, so I decided to keep it. Is that OK with you?

+                            blacklist_entries.size());
+  password_entries->insert(password_entries->end(), blacklist_entries.begin(),
+                           blacklist_entries.end());
+  blacklist_entries.weak_clear();
 
   if (!passwords_entry_map)
     return true;