We were trying to disassemble the whole body of a function, including
safepoints and the constant pool. This lead to DCHECK errors on mips.
This CL fixes that, and adds printing of source positions.
It also fixes the output of instructions size to only contain the
instructions for both on-the-heap and off-the-heap code.

R=titzer@chromium.org

Bug: chromium:800233
Change-Id: Idb15a779680af7997eb78aea2a329189b684d53e
Reviewed-on: https://chromium-review.googlesource.com/856458Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50444}