Rework ReadUnmapped(Self|Forked) to not need fork()
Rework ReadUnmapped(Self|Forked) to not need fork()

Avoids fork()ing as per previous tests in this file, necessary for
Fuchsia.

Unfortunately, I believe that mmap()/munmap() aren't actually working
correctly on Fuchsia as tested by the EXPECT_FALSE reads, and so these
tests incorrectly fail. Bug with repro filed upstream at ZX-1631.

Bug: crashpad:196, crashpad:215
Change-Id: Iec86f64fcee12097223326f2bf2d5a5348a8a610
Reviewed-on: https://chromium-review.googlesource.com/894124
Reviewed-by: Joshua Peraza <f5809a5e35ec7e1bd0e25cb0a0b68bb433cf6f17@chromium.org>
Reviewed-by: Mark Mentovai <f1b5a91d4d6ad523f2610114591c007e75d15084@chromium.org>
Commit-Queue: Scott Graham <e134406e1863f3b48b0795831afac5c0595efb36@chromium.org>

chromium/crashpad,chromium/crashpad,chromium/crashpad