Merged r13762 into 3.15 branch.

Make message listener API backwards compatible.

R=ulan@chromium.org
BUG=

Review URL: https://chromiumcodereview.appspot.com/12385080

git-svn-id: https://v8.googlecode.com/svn/branches/3.15@13796 ce2b1a6d-e550-0410-aec6-3dcde31c8c00