Avoid redundant setupPaintForDashPathEffect calls.

The previous changes to maintain SkPaint in Graphics context
resulted in excess calls to StrokeData::setupPaintForDashPathEffect
for the most common use case (dashed or dotted borders). This patch
makes it just one call per request for the paint.

R=fmalita@chromium.org
BUG=343240

Review URL: https://codereview.chromium.org/176883025

git-svn-id: svn://svn.chromium.org/blink/trunk@168692 bbb929c8-8fbe-4397-9dbb-9b2b20218538