Remove use of deprecated base::ListValue::Append(Value*) overload in //chrome/browser/ui/webui

BUG=581865
R=dpapad@chromium.org
TBR=dbeam@chromium.org

Review-Url: https://codereview.chromium.org/2415993002
Cr-Commit-Position: refs/heads/master@{#425136}
6 files changed