When optimizing SpeculativeToNumber we need to pay attention to the
hint, otherwise we optimize away a Signed32 conversion, based on the
fact that the input is a Number.

Bug: chromium:819298
Change-Id: I2ac7b0dac708fee9083eca2880bd5674a82daaa3
Reviewed-on: https://chromium-review.googlesource.com/955423Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51805}