The generated file only contained the last section of the module, since
the decoder's range is reset in DecodeSection.
This CL fixes this by remembering the original module bytes and dumping
them instead.

R=ahaas@chromium.org

Change-Id: I5e0f97279886817d58caac6114994bb9c1a147fc
Reviewed-on: https://chromium-review.googlesource.com/892980Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50953}