The heap traversal for SFI code objects when logging compiled functions
was previously accessing the abstract code of an SFI, logging its
bytecode if it exists or code object otherwise. However, there are some
(rare) cases where an SFI has both bytecode and a non-interpreter code
object -- for example, after baseline tier-up -- in which case we want
to log both, as both could be executing (at different points on the
stack).

BUG=v8:5758

Review-Url: https://codereview.chromium.org/2603333002
Cr-Commit-Position: refs/heads/master@{#42025}