Avoid handle dereference during graph optimization.

Avoid handle dereference during graph optimization.

With parallel recompilation enabled, objects made accessible by handles may
have changed between graph construction and graph optimization. Therefore
we must not assume that information on those objects remain the same between
those two phases. To police this, we forbid handle dereferencing during
graph optimization.
Exceptions to this rule are:
 - Dereferencing the handle to obtain the raw location of the object. This
   is safe since parallel recompilation acquires RelocationLock
 - Some places that dereference the handle for a type check. These are checked
   to be safe on a case-by-case basis.

R=jkummerow@chromium.org
BUG=

Review URL: https://chromiumcodereview.appspot.com/12049012

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13475 ce2b1a6d-e550-0410-aec6-3dcde31c8c00