This allows getting a heap object by a heap snapshot node for further
inspection. Very useful for objects from bindings that mostly have
getter-provided fields.

R=vegorov@google.com
BUG=webkit/61179
TEST=test-heap-profiler/GetHeapValue,GetHeapValueForDeletedObject

Review URL: http://codereview.chromium.org/8046006

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9430 ce2b1a6d-e550-0410-aec6-3dcde31c8c00