The class Float32 stores the bit pattern of a float as uint32_t to
guarantee that the exact bit pattern of the contained value is
preserved. This is necessary because the bit pattern of a NaN may
change, e.g. when it is passed as a parameter.

For convenience the Float32 class provides a constructor with a float
parameter. Since this constructor cannot guarantee that the right bit
pattern will be stored for NaNs, this CL adds a DCHECK now to make
sure that the constructor is never used with a NaN.

R=mstarzinger@chromium.org

Change-Id: Iba85a5a1bb2778d5f8bdc1aad97524ef8369b73d
Reviewed-on: https://chromium-review.googlesource.com/579367
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46811}