move patheffect virtuals to protected and rename

- change filterPath to safely handle if src and dst are aliases

Bug: skia:8254
Change-Id: I125d19404ca0a610f73271abb5c5455d1d50f9ed
Reviewed-on: https://skia-review.googlesource.com/147466
Commit-Queue: Mike Reed <reed@google.com>
Commit-Queue: Kevin Lubick <kjlubick@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Auto-Submit: Mike Reed <reed@google.com>
diff --git a/src/effects/SkDiscretePathEffect.cpp b/src/effects/SkDiscretePathEffect.cpp
index 46cd42b..2c913d8 100644
--- a/src/effects/SkDiscretePathEffect.cpp
+++ b/src/effects/SkDiscretePathEffect.cpp
@@ -81,8 +81,8 @@
     uint32_t fSeed;
 };
 
-bool SkDiscretePathEffect::filterPath(SkPath* dst, const SkPath& src,
-                                      SkStrokeRec* rec, const SkRect*) const {
+bool SkDiscretePathEffect::onFilterPath(SkPath* dst, const SkPath& src,
+                                        SkStrokeRec* rec, const SkRect*) const {
     bool doFill = rec->isFillStyle();
 
     SkPathMeasure   meas(src, doFill);