Fix UB function problems for shaders and mask.

include/core/SkShader.h

 /*
  * 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.
  */
 
 #ifndef SkShader_DEFINED
 #define SkShader_DEFINED
 
@@ skipping 131 matching lines @@
          */
         virtual uint8_t getSpan16Alpha() const { return fPaintAlpha; }
 
         /**
          *  Called for each span of the object being drawn. Your subclass should
          *  set the appropriate colors (with premultiplied alpha) that correspond
          *  to the specified device coordinates.
          */
         virtual void shadeSpan(int x, int y, SkPMColor[], int count) = 0;
 
-        typedef void (*ShadeProc)(void* ctx, int x, int y, SkPMColor[], int count);
+        /**
+         * The const void* ctx is only const because all the implementations are const.
+         * This can be changed to non-const if a new shade proc needs to change the ctx.
+         */
+        typedef void (*ShadeProc)(const void* ctx, int x, int y, SkPMColor[], int count);
         virtual ShadeProc asAShadeProc(void** ctx);
 
         /**
          *  Called only for 16bit devices when getFlags() returns
          *  kOpaqueAlphaFlag | kHasSpan16_Flag
          */
         virtual void shadeSpan16(int x, int y, uint16_t[], int count);
 
         /**
          *  Similar to shadeSpan, but only returns the alpha-channel for a span.
@@ skipping 276 matching lines @@
     SkMatrix fLocalMatrix;
 
     // So the SkLocalMatrixShader can whack fLocalMatrix in its SkReadBuffer constructor.
     friend class SkLocalMatrixShader;
     friend class SkBitmapProcShader;    // for computeTotalInverse()
 
     typedef SkFlattenable INHERITED;
 };
 
 #endif