DevTools: Extend EditableSettingsList to support <select> elements along with <input> for editing.

BUG=267592
R=vsevik

Review URL: https://codereview.chromium.org/361273003

git-svn-id: svn://svn.chromium.org/blink/trunk@177525 bbb929c8-8fbe-4397-9dbb-9b2b20218538