Previously the %_DateField intrinsic would also check the object and
throw an exception if you happen to pass something that is not a valid
JSDate, which (a) violates our policy for instrinsics and (b) is hard to
optimize in TurboFan (even Crankshaft has a hard time, but there we will
never inline the relevant builtins, so it doesn't show up). The throwing
part is now a separate intrinsics %_ThrowIfNotADate that throws an
exception in full codegen and deoptimizes in Crankshaft, which means the
code for the current use cases is roughly the same (modulo some register
renamings/gap moves).

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/1167813003

Cr-Commit-Position: refs/heads/master@{#28782}