Simplify the poly union.

src/core/SkLinearBitmapPipeline.h

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkLinearBitmapPipeline_DEFINED
 #define SkLinearBitmapPipeline_DEFINED
 
@@ skipping 11 matching lines @@
         SkFilterQuality filterQuality,
         SkShader::TileMode xTile, SkShader::TileMode yTile,
         const SkPixmap& srcPixmap);
     ~SkLinearBitmapPipeline();
 
     void shadeSpan4f(int x, int y, SkPM4f* dst, int count);
 
     template<typename Base, size_t kSize>
     class PolymorphicUnion {
     public:
-        PolymorphicUnion() {}
+        PolymorphicUnion() : fIsInitialized{false} {}
 
-        ~PolymorphicUnion() { get()->~Base(); }
+        ~PolymorphicUnion() {
+            if (fIsInitialized) {
+                get()->~Base();
+            }
+        }
 
         template<typename Variant, typename... Args>
         void Initialize(Args&&... args) {
             SkASSERTF(sizeof(Variant) <= sizeof(fSpace),
                       "Size Variant: %d, Space: %d", sizeof(Variant), sizeof(fSpace));
 
             new(&fSpace) Variant(std::forward<Args>(args)...);
+            fIsInitialized = true;
         };
 
         Base* get() const { return reinterpret_cast<Base*>(&fSpace); }
         Base* operator->() const { return get(); }
         Base& operator*() const { return *get(); }
 
     private:
         struct SK_STRUCT_ALIGN(16) Space {
             char space[kSize];
         };
+        bool fIsInitialized;
         mutable Space fSpace;
     };
 
     class PointProcessorInterface;
     class BilerpProcessorInterface;
     class PixelPlacerInterface;
 
     using MatrixStage = PolymorphicUnion<PointProcessorInterface, 112>;
     using FilterStage = PolymorphicUnion<PointProcessorInterface,   8>;
     using TileStage   = PolymorphicUnion<BilerpProcessorInterface, 96>;
     using SampleStage = PolymorphicUnion<BilerpProcessorInterface, 80>;
     using PixelStage  = PolymorphicUnion<PixelPlacerInterface,     80>;
 
 private:
     PointProcessorInterface* fFirstStage;
     MatrixStage fMatrixStage;
     FilterStage fFilterStage;
     TileStage   fTileXOrBothStage;
     TileStage   fTileYStage;
     SampleStage fSampleStage;
     PixelStage  fPixelStage;
 };
 
 #endif  // SkLinearBitmapPipeline_DEFINED