Fix issue 979.
Fix issue 979.

The issue is caused when deoptimizing to an internal AST ID in a
postfix increment or decrement operation on variable.  This could
happen for a global variable.  In that case, the optimized code was
not properly simulating an extra stack slot in the unoptimized code to
hold the original value.

Review URL: http://codereview.chromium.org/5871002

git-svn-id: b158db1e4b4ab85d4c9e510fdef4b1e8c614b15b@6025 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh