dom-v8: Adds virtual functions to ScriptWrappable.
dom-v8: Adds virtual functions to ScriptWrappable.

This is the first step to add virtual functions (vtbl) to ScriptWrappable.

This is part of a refactoring of DOM-V8 binding.  The design document is here:
https://docs.google.com/a/chromium.org/document/d/1uubaJGw0DVz0LwEEfHMVYBlrpFfoHzKyW60wBe6x58o/edit

BUG=235436

Review URL: https://codereview.chromium.org/370253002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@177973 bbb929c8-8fbe-4397-9dbb-9b2b20218538

primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs