r9540:
Don't count duplicate assignments to the same property as distinct ones.

In the ThisNamedPropertyAssignmentFinder, duplicate assignments to the same
property were counted as distinct assignments.  As a simple fix, subsequent
ones overwrite the previously recorded assignment.

This will reorder the assignments, but it is safe since they are restricted
to have only constants and parameters on the right-hand side (and there are
no assignments to the parameters).

r9562:
Add a regression test for an already fixed issue.

Add a regression test for Chromium issue 99167.

R=vegorov@chromium.org
BUG=
TEST=

Review URL: http://codereview.chromium.org/8218008

git-svn-id: http://v8.googlecode.com/svn/branches/3.4@9565 ce2b1a6d-e550-0410-aec6-3dcde31c8c00