GCC 4.9 used on some Node.js CI machines complains when the control
reaches the end of a non-void function and no return is encountered.

R=bmeurer@google.com, ofrobots@google.com, yangguo@google.com

Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: I5af0192cb187eccbf34dbb60ff3ac2e4774af803
Reviewed-on: https://chromium-review.googlesource.com/1105619Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53861}