Port 34225a6a

Original Commit Message:

    For spread calls with arrays with double elements but zero length,
    we skip the box-as-heapnumber step; so in this corner case the
    Call builtin sees a FixedDoubleArray, which is fine because it
    doesn't read any of the raw double values from it.
    This patch doesn't change the implementation, it only updates the
    assert to match reality.

R=jkummerow@chromium.org, joransiu@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=
LOG=N

Change-Id: Iafa52f21fb0bbee5656fdfd6c5f3a50894ff683f
Reviewed-on: https://chromium-review.googlesource.com/1126212Reviewed-by: Michael Dawson <michael_dawson@ca.ibm.com>
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#54227}