Previously this would result in applying trying to find a size modulo zero,
which causes SIGFPE. This approach was preferred over adding a default case
to preserve the ability of the compiler to detect unhandled switch cases
(within the valid range of the enum).

BUG=chromium:148757

Review-Url: https://codereview.chromium.org/2395073003
Cr-Commit-Position: refs/heads/master@{#40088}