Fix LayoutTest transitions/svg-transitions.html

The Web Animations implementation provides smooth interpolation to and from
'none' values for the SVG stroke-dasharray property, whereas the legacy
implementation does not. See https://codereview.chromium.org/26292004.

This is not speced, but the Web Animations behavior is preferred, so this
change updates the expected results accordingly.

R=timloh@chromium.org
BUG=303430

Review URL: https://codereview.chromium.org/39253004

git-svn-id: svn://svn.chromium.org/blink/trunk@160512 bbb929c8-8fbe-4397-9dbb-9b2b20218538