Refactor GenericBinaryOperation and its helper functions to always return a Result.

Refactor GenericBinaryOperation and its helper functions to always return a Result.

This is a preparation step for including number type information
in the virtual frame. We need a common place where we can update
the number type information of the result of a binary operation
since we should not modify the state of the virtual frame elements
directly.

Review URL: http://codereview.chromium.org/551080

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3661 ce2b1a6d-e550-0410-aec6-3dcde31c8c00