Make SkBlitter hierarchy explicit about what needs to be implemented.

src/core/SkBlitter.cpp

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBlitter.h"
 #include "SkAntiRun.h"
 #include "SkColor.h"
@@ skipping 20 matching lines @@
 }
 
 SkShader::Context* SkBlitter::getShaderContext() const {
     return nullptr;
 }
 
 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) {
         this->blitRect(x, y, 1, height);
     } else {
         int16_t runs[2];
         runs[0] = 1;
         runs[1] = 0;
 
         while (--height >= 0) {
@@ skipping 943 matching lines @@
     fShaderContext->~Context();
     SkShader::Context* ctx = fShader->createContext(rec, (void*)fShaderContext);
     if (nullptr == ctx) {
         // Need a valid context in fShaderContext's storage, so we can later (or our caller) call
         // the in-place destructor.
         new (fShaderContext) SkZeroShaderContext(*fShader, rec);
         return false;
     }
     return true;
 }