Make ShouldOverrideUrlLoadingInternal more readable (6 of N)

No functional changes intended, please revert if things break.

This function is a large, and hard to follow. I'm hoping to break out a
bunch of functions that are clearer about what they're doing and make
ordering clearer.

Bug: 1006927
Change-Id: I46f55b80979520453e7e1a9a79592a85735f98cc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1831944
Commit-Queue: Michael Thiessen <mthiesse@chromium.org>
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#701590}