Revert r11772: Add check for non-smi to the IL and use it for class checks.

Revert r11772: Add check for non-smi to the IL and use it for class checks.

In its current state this causes some performance regressions because
we can't eliminate non-smi checks properly in the optimizer.

TBR=vegorov@google.com
Committed: https://code.google.com/p/dart/source/detail?r=11774

[Vyacheslav Egorov (Google), 2012-09-03 16:58:25]

lgtm