Various cleanups in check elimination.

- Move IsMapAccess() to HObjectAccess.
- Collect the actual objects instead of HStoreNamedFields in
  effects, and also consider HTransitionElementsKind.
- Fix ownership of HCheckMaps::maps() and HLoadNamedField::maps().
- Avoid heavy copying of the same map sets all the time during
  check elimination, and do something useful with the memory
  instead by slightly bumping the maximum number of tracked
  objects.
- Slightly optimize UniqueSet::Contains().

R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/264693011

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21133 ce2b1a6d-e550-0410-aec6-3dcde31c8c00