The streaming decoder allocates the whole section buffer of the code
section when it reads the section length of the code section. Therefore
we have to check that the different parts of the code section actually
use all the bytes, and that the different parts of the code section do
not need more bytes than available. The check that all bytes are used
was missing in the case where the code section contained zero functions.

In addition, this CL adds some tracing to the streaming decoder which
may be useful in future debugging.

R=clemensh@chromium.org

Bug: chromium:783595
Change-Id: Icf056c25a3000b4a08a791939dab0ccde9fc3f80
Reviewed-on: https://chromium-review.googlesource.com/768788
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49380}