Revert "Improvements in positions handling in optimizing compiler." (r17765)

Original issue: https://codereview.chromium.org/49203002/

TBR=vegorov

Review URL: https://codereview.chromium.org/63343003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@17768 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Reland [Object.observe] Don't force normalization of elements for observed objects

Original Issue: https://codereview.chromium.org/29353003/

Note that this version of the patch includes logic for bailing out of compiled ArrayPush/ArrayPop calls if the array is observed (see stub-cache-*)

R=danno@chromium.org
BUG=v8:2946
LOG=N

Review URL: https://codereview.chromium.org/68343016

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@17769 ce2b1a6d-e550-0410-aec6-3dcde31c8c00