The collection builtins (Map, Set, WeakMap, WeakSet) are still written
in JavaScript and make heavy use of %_ClassOf, which is kind of
expensive compared to a simple instance type check. Change that to use
simple instance type checks instead.

R=jarin@chromium.org
BUG=v8:6261,v8:6278,v8:6344

Review-Url: https://codereview.chromium.org/2814773005
Cr-Commit-Position: refs/heads/master@{#45106}