Validation normally happens while generating the turbofan graph of a
wasm function. For lazy compilation (behind the flag
--wasm-lazy-compilation), we skip this graph generation step during
module generation. Thus we need to validate explicitely.

R=ahaas@chromium.org
BUG=chromium:724851

Change-Id: Ic70887c0d823460a272d0bb636dc98b2b7a7e55e
Reviewed-on: https://chromium-review.googlesource.com/509574Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45478}