ES6 symbols: Allow symbols as property names

ES6 symbols: Allow symbols as property names

Since symbols and strings share a common representation, most of this change is about consistently replacing 'String' with 'Name' in all places where property names are expected. In particular, no new logic at all is necessary for maps, property dictionaries, or transitions. :) The only places where an actual case distinction is needed have to do with generated type checks, and with conversions of names to strings (especially in logger and profiler).

Left in some TODOs wrt to the API: interceptors and native getters don't accept symbols as property names yet, because that would require extending the external v8.h.

(Baseline CL: https://codereview.chromium.org/12296026/)

R=verwaest@chromium.org,mstarzinger@chromium.org
BUG=v8:2158
Committed: http://code.google.com/p/v8/source/detail?r=13811

[Toon Verwaest, 2013-03-01 14:04:18]

lgtm