Clamp filter functions {grayscale, invert, opacity, sepia} to 100%

The spec says the following for these functions:

 "Values of amount over 100% are allowed but UAs must clamp the values
  to 1."

So do that rather than failing. This matches the behavior of Gecko and
Edge.

This fixes

http://test.csswg.org/suites/filters-1_dev/nightly-unstable/html/filter-grayscale-005.htm

from the CSS WG Filter Effects testsuite (w/ the property unprefixed.)

BUG=618607

Review-Url: https://codereview.chromium.org/2052883002
Cr-Commit-Position: refs/heads/master@{#399144}
4 files changed