Implement basic code generation for arrow functions

Implements code generation for arrow functions by desugaring them into
a FunctionLiteral. For the moment, a normal FUNCTION_SCOPE is used, so
"this" and "arguments" behave as in normal functions. Implementing the
correct scoping rules is to be done later on.

BUG=v8:2700
LOG=
R=rossberg@chromium.org

Review URL: https://codereview.chromium.org/382893003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22495 ce2b1a6d-e550-0410-aec6-3dcde31c8c00