Replace FilterData::filter with lastEffect

This brings the FilterData+SVGFilterPainter (etc)  "complex" closer to
the PaintLayer+PaintLayerFilterInfo structure by keep the last effect
in the chain and accessing the Filter through that when needed.
In general we want these two "complexes" to closely resemble each other
as possible - because they are supposed to implement the same thing, with
only a difference in the parametrization (like which bounding-box to use.)
This also brings one tiny (tiny tiny) step closer to being able to get
shorthand filters working in the SVG code-path.

Also try to reduce dependencies a bit in the surrounding code.

BUG=439970,109224
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Review-Url: https://codereview.chromium.org/2350063002
Cr-Commit-Position: refs/heads/master@{#419700}
4 files changed