Preivously this is disabled because quitting multiple windows could
bring up the unresponsive dialog, but since we now have increased the
unresponsive time limitto 5s, this is not needed anymore and could cause
confusions.

Fixes #17.

Fixes atom/atom#1841.

Fixes https://github.com/atom/atom/issues/1838.

The key-press signal captured the key events before renderer handles,
which violated the behavior on OS X and Windows.

Fixes #221.

Enable context menu in devtools

This allows us to reply to synchronous message for arbitrary
WebContents.