Make Object.freeze fast

This patch both speeds up the freeze operation itself, but also
allows properties to remain in fast mode. Objects with non-empty
elements backing stores still end up with slow elements.

Relanding r14758 and r14759 with fix for Test262: only mark properties
and elements READ_ONLY if they are not JS setter/getters. Tightened up
tests to assert frozen-ness, and added targeted tests for the new code
(covering accessors).

BUG=v8:1858, 115960
R=verwaest@chromium.org

Review URL: https://chromiumcodereview.appspot.com/15691007

Patch from Adam Klein <adamk@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14762 ce2b1a6d-e550-0410-aec6-3dcde31c8c00