Since the wasm module is verified before starting execution with lazy
compilation, the compilation of individual functions should not fail
later.
This CL changes the implementation to check this condition earlier
and removes unused error paths.

R=ahaas@chromium.org, mstarzinger@chromium.org
BUG=chromium:719286

Change-Id: If4bab457a47f214b457b2e2bc8570cba8c8bbcfd
Reviewed-on: https://chromium-review.googlesource.com/497755Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45161}