This refactors the way we (re)define elements to perform normalization
and attribute updating at a much deeper level, thereby removing some
bogus special cases in upper runtime layers.

Most element setters take an indicator flag that distinguishes between
setting and defining. Setting of an element causes attributes to remain
unchanged, writability to be checked and callbacks to be called.
Defining of an element causes attributes to be updated and callbacks to
be overridden. The same approach could be taken for properties.

R=svenpanne@chromium.org
BUG=v8:1772
TEST=test262,test262/15.2.3.6-4-333-11

Review URL: https://chromiumcodereview.appspot.com/9443014

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10808 ce2b1a6d-e550-0410-aec6-3dcde31c8c00