Cleanup SVGMarkerData::updateFromPathElement

Make the updateFromPathElement "closure" a simple thunk-style function,
to make it a little less unwieldy. Also pass PathElement& rather than
PathElement*.

BUG=633012,450368

Review-Url: https://codereview.chromium.org/2540513005
Cr-Commit-Position: refs/heads/master@{#434987}
1 file changed