We recently allowed global constants in asm.js validated code.
When used in a return statement, these need to be of an allowed type.

BUG=660813
R=jpp@chromium.org,aseemgarg@chromium.org

Review-Url: https://codereview.chromium.org/2481103002
Cr-Commit-Position: refs/heads/master@{#40850}