Avoid tagged values for Instructions that truncate the operands with ToNumber.

I case the ToNumber is applied to a non numeric value but its not observable (some constants and oddballs) we should already do it in hydrogen...

BUG=
R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/19798002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15818 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Eliminate map checks of constant values.

R=ulan@chromium.org

Review URL: https://chromiumcodereview.appspot.com/19954005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15819 ce2b1a6d-e550-0410-aec6-3dcde31c8c00