X87: Turn ToNumberStub into a PlatformCodeStub again.

port b6737c56eaf51d63ab83b6529f657c15f834623c (r25187)

original commit message:

  Turn ToNumberStub into a PlatformCodeStub again.

  The HydrogenCodeStub is too expensive and there's no easy way to reduce
  this cost, so turning it into a PlatformCodeStub solves that problem until
  we can use TurboFan for code stubs.

BUG=
R=weiliang.lin@intel.com

Review URL: https://codereview.chromium.org/714573003

Patch from Chunyang Dai <chunyang.dai@intel.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25227 ce2b1a6d-e550-0410-aec6-3dcde31c8c00