Add unit test for SVG path parsing
This converts svg/dom/path-parser.html into a roughly equivalent unit
test.
Widen the assert in the SVGPathStringSource constructor to allow "" but
not (null) Strings.
Also move the non-fuzzed tests from svg/dom/fuzz-path-parser.html.
BUG=
539385
Committed:
https://crrev.com/f47f8d15a10dff0acb74bb105aa514e5faf8612c
Cr-Commit-Position: refs/heads/master@{#355008}