Previously we were getting the code object from the stack, so printed incorrect
position details for interpreted frames.

BUG=v8:7916

Change-Id: I2f87584117d88b7db3f3b9bdbfe793c4d3e33fe9
Reviewed-on: https://chromium-review.googlesource.com/1126313Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54253}