Resubmit issue 2221103002 to fix the iOS build by declaring the flag in

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 53 matching lines @@
     }
 }
 
 void SkBlitter::blitRect(int x, int y, int width, int height) {
     SkASSERT(width > 0);
     while (--height >= 0) {
         this->blitH(x, y++, width);
     }
 }
 
-/// Default implementation doesn't check for any easy optimizations
-/// such as alpha == 0 or 255; also uses blitV(), which some subclasses
+/// Default implementation doesn't check for easy optimizations
+/// such as alpha == 255; also uses blitV(), which some subclasses
 /// may not support.
 void SkBlitter::blitAntiRect(int x, int y, int width, int height,
                              SkAlpha leftAlpha, SkAlpha rightAlpha) {
-    this->blitV(x++, y, height, leftAlpha);
+    if (leftAlpha > 0) { // we may send in x = -1 with leftAlpha = 0
+        this->blitV(x, y, height, leftAlpha);
+    }
+    x++;
     if (width > 0) {
         this->blitRect(x, y, width, height);
         x += width;
     }
-    this->blitV(x, y, height, rightAlpha);
+    if (rightAlpha > 0) {
+        this->blitV(x, y, height, rightAlpha);
+    }
 }
 
 //////////////////////////////////////////////////////////////////////////////
 
 static inline void bits_to_runs(SkBlitter* blitter, int x, int y,
                                 const uint8_t bits[],
                                 uint8_t left_mask, ptrdiff_t rowBytes,
                                 uint8_t right_mask) {
     int inFill = 0;
     int pos = 0;
@@ skipping 914 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;
 }