Unreviewed, rolling out r172741.
https://bugs.webkit.org/show_bug.cgi?id=136058

This change is breaking PLT. (Requested by mlam on #webkit).

Reverted changeset:

"REGRESSION(r172401): for-in optimization no longer works at
all"
https://bugs.webkit.org/show_bug.cgi?id=136056
http://trac.webkit.org/changeset/172741

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@172742 268f45cc-cd09-0410-ab3c-d52691b4dbfc
Unreviewed, rolling out r172736.
https://bugs.webkit.org/show_bug.cgi?id=136060

Caused 14% PLT regressions (Requested by rniwa on #webkit).

Reverted changeset:

"Remove PurgeableBuffer since it is not very useful any more"
https://bugs.webkit.org/show_bug.cgi?id=135939
http://trac.webkit.org/changeset/172736

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@172744 268f45cc-cd09-0410-ab3c-d52691b4dbfc