We in fact already access these via the private property "details_".
Make it into the API.

R=ulan@chromium.org, yurys@chromium.org, ulan, yangguo, yurys

Review URL: https://codereview.chromium.org/200243002

Patch from Andrey Adaykin <aandrey@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@19938 ce2b1a6d-e550-0410-aec6-3dcde31c8c00