We were not checking that the string passed to instantiateFromAsm
contains a function declaration (any declaration was allowed).
Fixes crash.
BUG=620649
BUG=v8:4203
R=aseemgarg@chromium.org
Review-Url: https://codereview.chromium.org/2109533002
Cr-Commit-Position: refs/heads/master@{#37349}
