Harden degenerate gradient context handling

src/effects/gradients/SkGradientShaderPriv.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkGradientShaderPriv_DEFINED
 #define SkGradientShaderPriv_DEFINED
 
@@ skipping 97 matching lines @@
     private:
         enum {
             kStorageCount = 16
         };
         SkColor4f fColorStorage[kStorageCount];
         SkScalar fPosStorage[kStorageCount];
         SkMatrix fLocalMatrixStorage;
         SkAutoMalloc fDynamicStorage;
     };
 
-public:
     SkGradientShaderBase(const Descriptor& desc, const SkMatrix& ptsToUnit);
     virtual ~SkGradientShaderBase();
 
     // The cache is initialized on-demand when getCache32 is called.
     class GradientShaderCache : public SkRefCnt {
     public:
         GradientShaderCache(U8CPU alpha, bool dither, const SkGradientShaderBase& shader);
         ~GradientShaderCache();
 
         const SkPMColor*    getCache32();
@@ skipping 23 matching lines @@
         static void Build32bitCache(SkPMColor[], SkColor c0, SkColor c1, int count,
                                     U8CPU alpha, uint32_t gradFlags, bool dither);
     };
 
     class GradientShaderBaseContext : public SkShader::Context {
     public:
         GradientShaderBaseContext(const SkGradientShaderBase& shader, const ContextRec&);
 
         uint32_t getFlags() const override { return fFlags; }
 
+        bool isValid() const;
+
     protected:
         SkMatrix    fDstToIndex;
         SkMatrix::MapXYProc fDstToIndexProc;
         uint8_t     fDstToIndexClass;
         uint8_t     fFlags;
         bool        fDither;
 
         SkAutoTUnref<GradientShaderCache> fCache;
 
     private:
@@ skipping 54 matching lines @@
      * Takes in pointers to gradient color and Rec info as colorSrc and recSrc respectively.
      * Count is the number of colors in the gradient
      * It will then flip all the color and rec information and return in their respective Dst
      * pointers. It is assumed that space has already been allocated for the Dst pointers.
      * The rec src and dst are only assumed to be valid if count > 2
      */
     static void FlipGradientColors(SkColor* colorDst, Rec* recDst,
                                    SkColor* colorSrc, Rec* recSrc,
                                    int count);
 
+    template <typename T, typename... Args>
+    static Context* CheckedCreateContext(void* storage, Args&&... args) {
+        auto* ctx = new (storage) T(std::forward<Args>(args)...);
+        if (!ctx->isValid()) {
+            ctx->~T();
+            return nullptr;
+        }
+        return ctx;
+    }
+
 private:
     enum {
         kColorStorageCount = 4, // more than this many colors, and we'll use sk_malloc for the space
 
         kStorageSize = kColorStorageCount *
                        (sizeof(SkColor) + sizeof(SkScalar) + sizeof(Rec) + sizeof(SkColor4f))
     };
     SkColor             fStorage[(kStorageSize + 3) >> 2];
 public:
     SkColor*            fOrigColors;   // original colors, before modulation by paint in context.
@@ skipping 251 matching lines @@
     GrGLSLProgramDataManager::UniformHandle fColorsUni;
     GrGLSLProgramDataManager::UniformHandle fFSYUni;
     GrGLSLProgramDataManager::UniformHandle fColorSpaceXformUni;
 
     typedef GrGLSLFragmentProcessor INHERITED;
 };
 
 #endif
 
 #endif