Drop PathParsingMode argument to buildStringFromByteStream

Just always produce a String with whatever format the input is.

Also cleanup some related code, and expose SVGPath from SVGPathElement
rather than the SVGPathByteStream.

BUG=467592

Review URL: https://codereview.chromium.org/1476283002

Cr-Commit-Position: refs/heads/master@{#361988}
7 files changed