This encapsulates message reporting into separate functions independent
from the logic of asm.js compilation and instantiation. It is mostly
refactoring with a small fix to also report successful instantiation of
the "single function" case.

R=clemensh@chromium.org

Change-Id: I89c2d62707e891bf51c19945c4067195f41290a4
Reviewed-on: https://chromium-review.googlesource.com/506195
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45362}