Fix: Fix frontend id property in passwords_private.idl

This property had the wrong naming convention in the idl file. So when
it was used in crrev.com/c/2219503, passwords_section started to
consider every password had the same frontend id and tried to merge
entries that were not really duplicates, causing the assertions in
MultiStorePasswordUiEntry to fail and no password to be displayed in
chrome://settings/passwords.

TBR=stevenjb@chromium.org

Bug: 1049141
Change-Id: Ic76b1f3ad574e02bec11c78bfe4a0425c911163f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2218318Reviewed-by: Marc Treib <treib@chromium.org>
Reviewed-by: Friedrich [CET] <fhorschig@chromium.org>
Reviewed-by: Jan Wilken Dörrie <jdoerrie@chromium.org>
Commit-Queue: Victor Vianna <victorvianna@google.com>
Cr-Commit-Position: refs/heads/master@{#773158}

chrome/common/extensions/api/passwords_private.idl

@@ -84,7 +84,7 @@ namespace passwordsPrivate {
 
     // An index to refer to an entry displayed by the UI. May correspond to
     // multiple entries in the backend.
-    long frontend_id;
+    long frontendId;
 
     // If true, the entry came from the Gaia-account-scoped password store
     // rather than from the profile-scoped one.
@@ -100,7 +100,7 @@ namespace passwordsPrivate {
 
     // An index to refer to an exception entry displayed by the UI. May
     // correspond to multiple entries in the backend.
-    long frontend_id;
+    long frontendId;
 
     // If true, the entry came from the Gaia-account-scoped password store
     // rather than from the profile-scoped one.