Using TruncateHeapNumberToI here simplifies the code and we get rid of ConvertToInt32 and EmitOutOfInt32RangeTruncate macro assembler instructions.

BUG=

Review URL: https://codereview.chromium.org/23444033
Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16505 ce2b1a6d-e550-0410-aec6-3dcde31c8c00