Remove the onMessage/onDisconnect listeners that the chrome.runtime.sendMessage
implementation adds to the Port it creates.
The underlying leak remains where any onMessage/onDisconnect listeners added to
a Port, but not removed, will be leaked when the Port goes out of scope; but at
least the most common case will be fixed.
BUG=320723
R=koz@chromium.org
Review URL: https://codereview.chromium.org/
76423003
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236301 0039d316-1c4b-4281-b951-d872f2087c98