Add a new, separate block entry instruction for catch-blocks.

Add a new, separate block entry instruction for catch-blocks.

This is a preparation CL for supporting try-catch in optimized code. Until
now, we used normal TargetEntryInstr for catch blocks.

This meant carrying around handler_types_ and catch_try_index_ for blocks
that are not catch blocks which is not needed.

For now, CatchBlockEntry behaves the same as TargetBlockEntry except for
the additional members needed for catch blocks.
Committed: https://code.google.com/p/dart/source/detail?r=19864

[Vyacheslav Egorov (Google), 2013-03-12 13:10:47]

lgtm

[Florian Schneider, 2013-03-12 13:51:38]

Committed patchset #2 manually as r19864 (presubmit successful).