Align SameSizeAsFillLayer with FillLayer

After http://crrev.com/35303002/ added a bit in FillLayer, it was
discovered that SameSizeAsFillLayer was slightly out-of-date (by 11
bits). Remove ambition to track the number of used bits in each bit
field since it easily goes out-of-date and doesn't serve a useful
purpose.

BUG=304721

Review URL: https://codereview.chromium.org/37223002

git-svn-id: svn://svn.chromium.org/blink/trunk@164932 bbb929c8-8fbe-4397-9dbb-9b2b20218538