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This changes the path used for invalidation of filter effects (SVGFE*)
from the layout tree to the DOM tree. This is done to allow invalidation
to work when the filter is not part of the layout tree. That change
will be done in a follow-up.

Also add casting helpers for SVGFilterPrimitiveStandardAttributes and
use it where applicable.

Bug: 773811
Change-Id: I275534e59eb285c0cab805f6c09d00b1f725e4f4
Reviewed-on: https://chromium-review.googlesource.com/719837Reviewed-by: Stephen Chenney <schenney@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Commit-Queue: Philip Rogers <pdr@chromium.org>
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#509478}