Introducing machine operators early causes trouble for the typing,
truncation analysis and representation selection, so we should rather
stick to simplified operators instead. Now there's only the for-in case
left, which is not clear how we can handle this in a better way.

Drive-by-fix: Also don't introduce Int32Constant and Word32Shl in
JSTypedLowering, but use NumberConstant and proper NumberShiftLeft
operators instead.

R=jarin@chromium.org
BUG=chromium:630951

Review-Url: https://codereview.chromium.org/2182453002
Cr-Commit-Position: refs/heads/master@{#38008}