EventSender::contextClick leaks NPObject used as its return value, leading to a leak of DOMWindow.

BUG=None

Review URL: https://chromiumcodereview.appspot.com/22548008

git-svn-id: svn://svn.chromium.org/blink/trunk@155772 bbb929c8-8fbe-4397-9dbb-9b2b20218538