Make event logger slightly more light-weight.

R=dcarney@chromium.org
BUG=chromium:423668
LOG=N

Review URL: https://codereview.chromium.org/651413002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24624 ce2b1a6d-e550-0410-aec6-3dcde31c8c00