Refactor the length functions to remove passing around the extra bool parameter for rounding behavior that is only used in a few places.

BUG=None

Review URL: https://codereview.chromium.org/122973002

git-svn-id: svn://svn.chromium.org/blink/trunk@164471 bbb929c8-8fbe-4397-9dbb-9b2b20218538