allow one zero length dash

src/effects/SkDashPathEffect.cpp

Index: src/effects/SkDashPathEffect.cpp
diff --git a/src/effects/SkDashPathEffect.cpp b/src/effects/SkDashPathEffect.cpp
index ced0aab69a9930efbbd216127f776dd5d8c2770d..38164999159176a59bc49baf7930179b02309fd9 100644
--- a/src/effects/SkDashPathEffect.cpp
+++ b/src/effects/SkDashPathEffect.cpp
@@ -14,7 +14,7 @@
 
 SkDashPathEffect::SkDashPathEffect(const SkScalar intervals[], int count, SkScalar phase)
         : fPhase(0)
-        , fInitialDashLength(0)
+        , fInitialDashLength(-1)
         , fInitialDashIndex(0)
         , fIntervalLength(0) {
     SkASSERT(intervals);
@@ -23,7 +23,6 @@ SkDashPathEffect::SkDashPathEffect(const SkScalar intervals[], int count, SkScal
     fIntervals = (SkScalar*)sk_malloc_throw(sizeof(SkScalar) * count);
     fCount = count;
     for (int i = 0; i < count; i++) {
-        SkASSERT(intervals[i] >= 0);
         fIntervals[i] = intervals[i];
     }
 
@@ -38,7 +37,7 @@ SkDashPathEffect::~SkDashPathEffect() {
 
 bool SkDashPathEffect::filterPath(SkPath* dst, const SkPath& src,
                               SkStrokeRec* rec, const SkRect* cullRect) const {
-    return SkDashPath::FilterDashPath(dst, src, rec, cullRect, fIntervals, fCount,
+    return SkDashPath::InternalFilter(dst, src, rec, cullRect, fIntervals, fCount,
                                       fInitialDashLength, fInitialDashIndex, fIntervalLength);
 }
 
@@ -162,7 +161,7 @@ bool SkDashPathEffect::asPoints(PointData* results,
                                 const SkMatrix& matrix,
                                 const SkRect* cullRect) const {
     // width < 0 -> fill && width == 0 -> hairline so requiring width > 0 rules both out
-    if (fInitialDashLength < 0 || 0 >= rec.getWidth()) {
+    if (0 >= rec.getWidth()) {
         return false;
     }
 
@@ -388,13 +387,8 @@ void SkDashPathEffect::toString(SkString* str) const {
 //////////////////////////////////////////////////////////////////////////////////////////////////
 
 SkPathEffect* SkDashPathEffect::Create(const SkScalar intervals[], int count, SkScalar phase) {
-    if ((count < 2) || !SkIsAlign2(count)) {
+    if (!SkDashPath::ValidDashPath(phase, intervals, count)) {
         return nullptr;
     }
-    for (int i = 0; i < count; i++) {
-        if (intervals[i] < 0) {
-            return nullptr;
-        }
-    }
     return new SkDashPathEffect(intervals, count, phase);
 }