constant_pool_offset can be equal to InstructionSize if the code doesn't
contains any extra entries.

Change-Id: I7340a0581cc9d97a802406b6c099412d38a673fc
Reviewed-on: https://chromium-review.googlesource.com/c/1412494Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#58835}