MIPS: cleanup api callbacks now that handles are never returned directly

Port r16360 (72401868)

BUG=

Review URL: https://codereview.chromium.org/23604004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16373 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
MIPS: Eliminate intentional conversion from Smi to Int32 in HMul

Port r16361 (b41ab14c)

Original commit message:
If not all uses of arithmetic binary operation can be truncated to Smi, check if they can be truncated to Int32 which could avoid minus zero check

Fixed DoMulI on X64 to adopt correct operand size when the representation is Smi

Fixed DoMulI on ARM. Constant right operand optimization is based on Integer 32 instead of its representation.

BUG=

Review URL: https://codereview.chromium.org/23644002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16374 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
MIPS: Eliminate Smi check when changing from Smi to Integer32

Port r16362 (6dd68a5c)

BUG=

Review URL: https://codereview.chromium.org/23462004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16375 ce2b1a6d-e550-0410-aec6-3dcde31c8c00