Use ScopedRunnableMethodFactory in WebSocketJob

Don't post SendPending if it is already posted.

BUG=89795
TEST=none

Review URL: http://codereview.chromium.org/7488007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@93599 0039d316-1c4b-4281-b951-d872f2087c98