This adds a dedicated test to make sure we don't try constant folding on
checks (in this case CheckTaggedPointer), which would generate invalid
code as we removing checks that guard the constant without knowing
whether it's safe to do so.
R=jarin@chromium.org
Review-Url: https://codereview.chromium.org/2087153002
Cr-Commit-Position: refs/heads/master@{#37168}
