For OOB checks on memory accesses, we first subtracted the size of the
type to load/store from the memory size, and then compared against this
effective_size. If the memory size is smaller than the size of the type,
this would lead to an integer underflow, and we would try to load the
value.
This CL fixes this, and adds a test case for this.

R=ahaas@chromium.org
BUG=v8:5822

Change-Id: I26fcba0be7343c88b8459d029b0c0af095d2466a
Reviewed-on: https://chromium-review.googlesource.com/465946
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44345}