Causes crashes on canary if there is a GC and the value makes it onto
the stack.

Bug: chromium:727662
Change-Id: I44fa8cf8a83b43d64418896c0a1f5518401b454f
Reviewed-on: https://chromium-review.googlesource.com/519302Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45623}