MIPS: Use AST's type field and merge types for unary, binary & compare ICs.

Port r15264 (d4c3767)

Missing fixed_right_arg().has_value cases added also.

BUG=

Review URL: https://codereview.chromium.org/17552008
Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15273 ce2b1a6d-e550-0410-aec6-3dcde31c8c00