To test the upcoming changes for map sharing in the presence of accessors, it is
essential that we keep a few global invariants: The map tree should always stay
a tree and AccessorPairs should not be shared between different DescriptorArrays
and/or StringDictionaries. This CL adds a test method for the latter invariant
and makes some changes to the bootstrapping process to avoid such sharing.

Note that we can't enable the new test method permanently yet, because we
currently go back and forth between fast mode and slow mode when adding an
accessor and break this invariant temporarily. This will be handled in a
separate CL.

Review URL: https://chromiumcodereview.appspot.com/9417043

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10744 ce2b1a6d-e550-0410-aec6-3dcde31c8c00