port 666aec03 (r34237)

  original commit message:
  Since both null and undefined are also marked as undetectable now, we
  can just test that bit instead of having the CompareNilIC try to collect
  feedback to speed up the general case (without the undetectable bit
  being used).

  Drive-by-fix: Update the type system to match the new handling of
  undetectable in the runtime.

BUG=

Review URL: https://codereview.chromium.org/1731383003

Cr-Commit-Position: refs/heads/master@{#34270}