[turbofan] Lower asm.js truncations to JSToNumber.

- JSBitwiseOr(x, 0) => Word32Or(NumberToInt32(JSToNumber(x)), 0)
- JSMultiply(x, 1) => NumberMultiply(JSToNumber(x), 1)

R=jarin@chromium.org

Review URL: https://codereview.chromium.org/706863003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25198 ce2b1a6d-e550-0410-aec6-3dcde31c8c00