We'll take expressions like typeof 'hello' and reduce it to 'string'.
Neat! This CL moves the optimization to an explicit reduction
in typed lowering that inserts a constant string, instead of
relying on type matching.

BUG=

Review-Url: https://codereview.chromium.org/2411703002
Cr-Commit-Position: refs/heads/master@{#40175}