MIPS: Implement Polymorphic Store ICs.

Port r15566 (a76585e)

Original commit message:
- Makes a common superclass for Load and Store stub compiler.
- Splits all non-normal Store ICs into handler and IC.
- Ensures monomorphic store ICs go polymorphic.
- Feeds polymorphic type feedback into count operation.

BUG=

Review URL: https://codereview.chromium.org/18595006
Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15576 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
MIPS: Do not omit the write-barrier if the input value is a smi.

Port r15573 (3954d53)

Original commit message:
ARM: Do not omit the write-barrier if the input value is a smi.
The input value isn't what is written into the field if the representation is double. A heap-number is written to the field instead; which requires a write-barrier.

BUG=chromium:254570

Review URL: https://codereview.chromium.org/18118010
Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15577 ce2b1a6d-e550-0410-aec6-3dcde31c8c00