Restructure the code a little, and change how we detect sloppy block function
redeclaration so we don't dereference a possibly nullptr function.

Bug: chromium:900786
Change-Id: Ief124fe767603ca36f4dc8865c4aeb3e0635b4cf
Reviewed-on: https://chromium-review.googlesource.com/c/1314331Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57206}