For values with canonical representation (i.e. not Number, Simd128Value
or Number) we can turn a strict equality comparison to a direct pointer
comparison. This removes the weird performance cliff when using a null
or undefined constant instead of the literals.

R=jarin@chromium.org
BUG=v8:5042

Review-Url: https://codereview.chromium.org/2027603002
Cr-Commit-Position: refs/heads/master@{#36612}