Define WebFilterAnimationCurve

This defines WebFilterAnimationCurve, needed for sending
filter animations from Blink to cc.

BUG=181613

Review URL: https://codereview.chromium.org/25345002

git-svn-id: svn://svn.chromium.org/blink/trunk@159082 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Reland Revert "Revert 157959 "Introduce a new reference graph to SVG*TearOffs.""

Reland the patches. All known SVGProperty memory bugs were resolved.

SVGAnimatedListPropertyTearOff::clearAnimatedProperty modified to not detachListWrappers(). "clearAnimatedProperty" is only called from ~SVGElement and the context SVGElement is guaranteed to be alive while a tearoff is alive. There was no need to detachListWrappers to keep the list item tearoffs valid.

BUG=270000
BUG=294464

R=pdr@chromium.org,haraken@chromium.org,inferno@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=158679

Review URL: https://codereview.chromium.org/25461003

git-svn-id: svn://svn.chromium.org/blink/trunk@159083 bbb929c8-8fbe-4397-9dbb-9b2b20218538