We can constant-fold ReferenceEqual(a,b) to false, if the intersection
of the types of a and b is empty. This also repairs a regression in the
RestParameter performance test.

R=petermarshall@chromium.org
BUG=chromium:686668

Review-Url: https://codereview.chromium.org/2666543002
Cr-Commit-Position: refs/heads/master@{#42775}