Instead of creating a new character stream to re-parse the asm.js module,
use the existing stream which was used by the parser.  By doing this, we
avoid accessing the heap if the original character stream is a streaming
source or an external string, which will enable asm.js verification to run
off-thread in those situations.

BUG=v8:5203

Change-Id: I5dbf83c993512eb2f3dd709120e152e3f9900bdf
Reviewed-on: https://chromium-review.googlesource.com/616723Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47500}