The Float32(uint32_t) constructor should not be public, use
Float32::FromBits explicitly if needed.

R=ahaas@chromium.org

Change-Id: I414e621deebde8cdb474f17e08fcc489dbc083cd
Reviewed-on: https://chromium-review.googlesource.com/738173Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48934}