This fixes printing of {CallRuntime} nodes that are backed by JavaScript
functions. Issues with the printing that was in place:
 - Crash because it was accessing {context} instead of {native_context}
 - Printout was not comparable, raw heap pointer different between runs

R=bmeurer@chromium.org

Change-Id: I941944b46550bd908ec14a324bc255d6c8f96fbe
Reviewed-on: https://chromium-review.googlesource.com/464766Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44298}