Add constructor to DashInfo to enable initializer lists

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2230143003

Review-Url: https://codereview.chromium.org/2230143003

include/core/SkPathEffect.h

@@ -118,6 +118,8 @@ public:
 
     struct DashInfo {
         DashInfo() : fIntervals(NULL), fCount(0), fPhase(0) {}
+        DashInfo(SkScalar* intervals, int32_t count, SkScalar phase)
+            : fIntervals(intervals), fCount(count), fPhase(phase) {}
 
         SkScalar*   fIntervals;         //!< Length of on/off intervals for dashed lines
                                         //   Even values represent ons, and odds offs