Make SkBlitter hierarchy explicit about what needs to be implemented.

src/core/SkBlitter.cpp

Index: src/core/SkBlitter.cpp
diff --git a/src/core/SkBlitter.cpp b/src/core/SkBlitter.cpp
index 343160c4b4b8a6f6660abc18e57e84983b80d743..daced55ef2ed33d3fd2a941394468b135980edec 100644
--- a/src/core/SkBlitter.cpp
+++ b/src/core/SkBlitter.cpp
@@ -38,14 +38,17 @@ const SkPixmap* SkBlitter::justAnOpaqueColor(uint32_t* value) {
     return nullptr;
 }
 
+/*
 void SkBlitter::blitH(int x, int y, int width) {
     SkDEBUGFAIL("unimplemented");
 }
 
+
 void SkBlitter::blitAntiH(int x, int y, const SkAlpha antialias[],
                           const int16_t runs[]) {
     SkDEBUGFAIL("unimplemented");
 }
+ */
 
 void SkBlitter::blitV(int x, int y, int height, SkAlpha alpha) {
     if (alpha == 255) {