Remove kDisableArbitraryScaleFactorInImageSkia flag.

it's been enabled for 3 milestones.

BUG=None
R=oshima@chromium.org
TBR=asvitkine@chromium.org
TEST=none

Review URL: https://codereview.chromium.org/633663002

Cr-Commit-Position: refs/heads/master@{#298521}
5 files changed