For memory limit checks, we should use the minimum of the
--wasm-max-mem-pages flag and kV8MaxWasmMemoryPages. The former is a
limit set by the user, the latter is the maximum we can handle
internally.

R=titzer@chromium.org

Bug: chromium:898677
Change-Id: I3c549f4e90dd016b5d07475d9353f30134f76dcc
Reviewed-on: https://chromium-review.googlesource.com/c/1305274
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57127}