[iOS][Credential-Provider] Adds debug info.

Log `localizedDescription` instead of `description`.
Log the code of the error.

Bug: 1091927
Change-Id: Iea21882a5847741fbe19196549c2deeda4f24234
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2270440
Commit-Queue: Javier Ernesto Flores Robles <javierrobles@chromium.org>
Commit-Queue: Mark Cogan <marq@chromium.org>
Auto-Submit: Javier Ernesto Flores Robles <javierrobles@chromium.org>
Reviewed-by: Mark Cogan <marq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#783050}

ios/chrome/browser/credential_provider/credential_provider_service.mm

@@ -65,8 +65,9 @@ void SyncASIdentityStore(ArchivableCredentialStore* credential_store) {
                                        initWithCredential:credential]];
       }
       auto replaceCompletion = ^(BOOL success, NSError* error) {
-        DCHECK(success) << "Failed to update store, error: "
-                        << base::SysNSStringToUTF8(error.description);
+        DCHECK(success) << "Failed to update store, error description: "
+                        << base::SysNSStringToUTF8(error.localizedDescription)
+                        << ", error code: " << error.code;
         NSUserDefaults* shared_defaults = app_group::GetGroupUserDefaults();
         NSString* key =
             kUserDefaultsCredentialProviderASIdentityStoreSyncCompleted;