Fix nativeMessaging example to use chrome.runtime namespace.

Previously the example was calling chrome.extension.connectNative().

BUG=
R=mpcomplete@chromium.org

Review URL: https://codereview.chromium.org/27556002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228976 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228976