Use StylePath instead of (Path)StyleMotionPath
Replace uses of PathStyleMotionPath with StylePath and remove the former
as well as the StyleMotionPath base-class. The methods length() and
isClosed() are transferred to StylePath.
Pass const CSSValue& to StyleBuilderConverter::convertPath (fixup to
https://codereview.chromium.org/1545713003) necessitating mutability.
Convert motion-path style building to use a converter.
BUG=
535429
Committed:
https://crrev.com/7b3f2bb9e1638f6a5c6189a484c6e63f329a18da
Cr-Commit-Position: refs/heads/master@{#372643}