Deoptimize to the proper target after assignment side effects.

Deoptimize to the proper target after assignment side effects.

This fixes V8 issue 989.

Before, assignments used the AST ID of the assignment expression to
mark the side effect of the store, which became a target for
deoptimization bailout for code after the assignment.  In effect
contexts this environment included the value of the assignment, which
was unexpected by the unoptimized code.

Now we introduce a new assignment ID for AST node types that include
an assignment (Assignment, CountOperation, and ForInStatement) and use
it for the side effect of the store.

Committed: http://code.google.com/p/v8/source/detail?r=5990

[fschneider, 2010-12-13 16:22:59]

LGTM.