Experimental: add a pre-merge step to perform some frame moves that do...

Experimental: add a pre-merge step to perform some frame moves that do
not require code generation (X-to-memory where X is synced and
X-to-invalid).

This allows us to catch more empty merge-code blocks and combine more
non-empty blocks.

Committed: http://code.google.com/p/v8/source/detail?r=1320

[William Hesse, 2009-02-19 14:37:08]

LGTM.