Samples taken during deoptimization require care in the stack walk
used to gather frames. The top N stack frames may not have JSFunction
objects in place, because those frames represent inlined functions
which may not have closures yet.

Bug: v8:7314
Change-Id: Ib6488aee46a47d5341cab1b1c9c3851592ba6509
Reviewed-on: https://chromium-review.googlesource.com/870036
Commit-Queue: Ali Ijaz Sheikh <ofrobots@google.com>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Ali Ijaz Sheikh <ofrobots@google.com>
Cr-Commit-Position: refs/heads/master@{#50732}