PasswordStore: Clean up expectations about rewriting vectors of forms

chrome/browser/password_manager/password_store_x.h

Index: chrome/browser/password_manager/password_store_x.h
diff --git a/chrome/browser/password_manager/password_store_x.h b/chrome/browser/password_manager/password_store_x.h
index 17655338947e9e334451ecc023feb1e1f5824ae8..000d4af0ace3ed15d864e78b8a2968366a8ffd84 100644
--- a/chrome/browser/password_manager/password_store_x.h
+++ b/chrome/browser/password_manager/password_store_x.h
@@ -58,6 +58,10 @@ class PasswordStoreX : public password_manager::PasswordStoreDefault {
         base::Time delete_end,
         password_manager::PasswordStoreChangeList* changes) = 0;
 
+    // The three methods below overwrite |forms| with all stored credentials
+    // matching |form|, all stored non-blacklisted credentials, and all stored
+    // blacklisted credentials, respectively. On success, they return true,
+    // otherwise they return false and erase |forms|.
     virtual bool GetLogins(const autofill::PasswordForm& form,

[engedy, 2015/02/25 15:17:48]

The FailingBackend in password_store_x_unittest.cc should clear |forms| too. (3
methods.)

[vabr (Chromium), 2015/03/09 10:56:19]

Done.
After dropping the promise about erasing on failure in the comment above, this
is was no longer needed, but I added the clearing calls to the FailingBackend as
well. I'm not entirely sure whether it is actually an improvement (maybe keeping
possible garbage there would help discover the callsite relying on non-existing
promises), but neither clearing, nor keeping seemed like the ideal choice.

[engedy, 2015/03/09 13:33:17]

Acknowledged.

                            ScopedVector<autofill::PasswordForm>* forms) = 0;
     virtual bool GetAutofillableLogins(