Add accumulate argument to PathAnimationEffect constructor
Add accumulate argument to PathAnimationEffect constructor

This allows the accumulation attribute of a PathAnimationEffect to be set,
which previously was not possible.

Note that the patch [1] to fix this in the spec narrowly missed FPWD.

[1] https://dvcs.w3.org/hg/FXTF/rev/f55c175711df

beni55/web-animations-js-legacy,birtles/web-animations-js,web-animations/web-animations-js-legacy,beni55/web-animations-js-legacy,birtles/web-animations-js,beni55/web-animations-js-legacy,beni55/web-animations-js-legacy,web-animations/web-animations-js-legacy,web-animations/web-animations-js-legacy,birtles/web-animations-js