This avoids redundant casts, loss of precision, and potential overflows.

BUG=chromium:597310
LOG=NO

Review URL: https://codereview.chromium.org/1841043002

Cr-Commit-Position: refs/heads/master@{#35113}

BUG=chromium:490559
LOG=NO

Review URL: https://codereview.chromium.org/1352453004

Cr-Commit-Position: refs/heads/master@{#30944}