Add WTF_LOG_ALWAYS and use it in PrivateScriptRunner

Currently fprintf is the only way to log errors in both debug and release builds.
This CL adds a WTF_LOG_ALWAYS macro that logs errors in both builds.

BUG=341031

Review URL: https://codereview.chromium.org/457543002

git-svn-id: svn://svn.chromium.org/blink/trunk@179800 bbb929c8-8fbe-4397-9dbb-9b2b20218538