MIPS: Elide hole checks on KeyedLoads of holey double arrays

Port r14630 (124d01e7)

Original commit message:
Improves NavierStokes by about 5%

BUG=

Review URL: https://codereview.chromium.org/14762012

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14651 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
MIPS: Only flush SharedFunctionInfo optimized code cache when necessary

Port r14650 (d045fbd3)

BUG=

Review URL: https://codereview.chromium.org/15035007

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14652 ce2b1a6d-e550-0410-aec6-3dcde31c8c00