Fix build issue in Debug mode
Fix build issue in Debug mode

Build error:
input_handler_proxy.cc:610:1: error: control reaches end of non-void
function [-Werror=return-type]

BUG=

Review URL: https://codereview.chromium.org/1631563002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#371523}

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk