MIPS: Move state sentinels into TypeFeedbackVector.

Port r24037 (d821bf9)

Original commit message:
These sentinels were in the wrong place, living in only tangentially related class TypeFeedbackInfo, but they codify state in the TypeFeedbackVector.

BUG=
R=dusan.milosavljevic@imgtec.com

Review URL: https://codereview.chromium.org/583573003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24046 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
MIPS: Convert KeyedLoad indexed interceptor case to a Handler.

Port r24042 (eb9b9ec)

Original commit message:
Currently, KeyedLoads on objects with indexed interceptors are handled with a
special stub. Instead, key on the map and handler mechanism for more uniform
treatment.

BUG=
R=dusan.milosavljevic@imgtec.com

Review URL: https://codereview.chromium.org/579273002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24047 ce2b1a6d-e550-0410-aec6-3dcde31c8c00