Reland "Avoid some unnecessary fast-properties map creations."

This relands commit ea74f0f85a7730879a2f17721629f93525886092.

The revert was due to failures in cctest/test-heap/ReleaseOverReservedPages,
caused by apparent changes to memory layout and fragmentation of the
first page. Eliminating a situation in messages.js where this CL has had
an effect on map transitions seems to solve the issue.

R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/714883003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25266 ce2b1a6d-e550-0410-aec6-3dcde31c8c00