hterm: Add optional timeout parameter to Terminal.showOverlay.
hterm: Add optional timeout parameter to Terminal.showOverlay.

BUG=none
TEST=test_harness.html, 55/55 tests passed.

Change-Id: I79a2a11d746ae024b8c42d3c856e48d7be6acfea
Reviewed-on: https://gerrit.chromium.org/gerrit/16765
Reviewed-by: Marius Schilder <d423f2980be0298efdef7df239b147d21d472f26@google.com>
Commit-Ready: Marius Schilder <d423f2980be0298efdef7df239b147d21d472f26@google.com>
Reviewed-by: Zelidrag Hornung <2423ba2b026624ad482ad8e6887b2d657f9c0c43@chromium.org>
Commit-Ready: Robert Ginda <4419ac4e35d191308e944202d542b192188656d1@chromium.org>
Tested-by: Robert Ginda <4419ac4e35d191308e944202d542b192188656d1@chromium.org>

chromium/hterm,chromium/hterm,chromium/hterm,chromium/hterm