Refactoring:
  move 'class Runtime' from 'runtime' to 'kernel'
  add 'class Context' and 'class Arena' to 'class Runtime' as a nested class
Runtime APIs:
  JavaScriptCore, StackFrame/List/Map APIs
Runtime APIs:
  JavaScriptCore, Class/Enum APIs
Runtime APIs:
  JavaScriptCore, Property/Method/ClassRegistry APIs