There are a couple of operators that can indeed produce Float32
representation, which we might end up using in a TaggedSigned
context, so add the missing conversion (indirectly via Float64).

BUG=chromium:656275
R=jarin@chromium.org

Review-Url: https://codereview.chromium.org/2421193002
Cr-Commit-Position: refs/heads/master@{#40334}