Also add support for JSFunction::prototype and JSString::length
accessors to CodeStubAssembler::CallGetterIfAccessor and remove
the special case hack from the LoadIC_Uninitialized.

Also address the TODO to unify the implementation with the
LoadIC_FunctionPrototype handler.

BUG=v8:5269,v8:6325
R=ishell@chromium.org

Change-Id: Ic51221e35a051c403d3a86dc41213c913e8f9d85
Reviewed-on: https://chromium-review.googlesource.com/489946
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44964}