Fix uninitialized fields in the BinaryOperation ast node.

R=jkummerow@chromium.org, svenpanne@chromium.org
BUG=chromium:429194
LOG=n

Review URL: https://codereview.chromium.org/701533002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25077 ce2b1a6d-e550-0410-aec6-3dcde31c8c00