This drops the %_ValueOf intrinsic, but keeps the runtime entry
%ValueOf for now, by either migrating the functionality (mostly
Debug mirror or toString/valueOf methods) to C++ or TurboFan
builtins, or switching to the %ValueOf runtime call when it's
not performance critical anyways.

The %_ValueOf intrinsic was one of the last blockers for fixing
the unsound machine operator typing in TurboFan.

R=yangguo@chromium.org
BUG=v8:5049

Review-Url: https://codereview.chromium.org/2126453002
Cr-Commit-Position: refs/heads/master@{#37512}