In this CL I implement streaming compilation for WebAssembly,
as described in the design doc I have sent out already.

In this implementation the decoding of sections other than the
code section is done immediately on the foreground thread.
Eventually all decoding should happen in the background. I
think it is acceptable to do the decoding on the foreground
thread for now because I have finished it already, and
decoding in the background would add even more complexity to
this CL.

Bug:v8:6785

Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: I285e1e5e1a5a243113c92571b25ee9bae551d0ed
Reviewed-on: https://chromium-review.googlesource.com/631721Reviewed-by: Mircea Trofin <mtrofin@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48022}