Streamline JumpTarget::ComputeEntryFrame by removing the separate loop

Streamline JumpTarget::ComputeEntryFrame by removing the separate loop
that sets the static type on elements in the entry frame.  Instead set
the static type as early as possible when computing elements.

Because the elements are shared with the reaching frames, this has the
side effect of sometimes changing the static type of reaching frame
elements.  They will be changed anyway in VirtualFrame::PrepareMergeTo
immediately after, so this is safe.

Review URL: http://codereview.chromium.org/113258

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1928 ce2b1a6d-e550-0410-aec6-3dcde31c8c00