Unprefix the CSS 'filter' property

Parse 'filter' in the same way as '-webkit-filter', and make the latter
an alias of the former.
For SVG content, only the "url(...)" function is allowed still, with the
exception of the outermost <svg> (LayoutSVGRoot), since that "has a box".

Update tests to use 'filter' where reasonable and applicable.

Intent to Ship: https://groups.google.com/a/chromium.org/d/topic/blink-dev/ZVT2kxuFMaA/discussion

Based on https://codereview.chromium.org/1987943002 by noel@chromium.org.

BUG=613441,618160,550249,535786,244295,109224

Review-Url: https://codereview.chromium.org/2065593002
Cr-Commit-Position: refs/heads/master@{#400752}
84 files changed