Implement Fill() for incomplete decodes to RGBA_F16

src/codec/SkPngCodec.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCodec.h"
 #include "SkColorSpaceXform.h"
 #include "SkColorTable.h"
@@ skipping 25 matching lines @@
 
         explicit operator bool() const { return fPtr != nullptr; }
 
         void* fPtr;
     };
 
     Result onGetPixels(const SkImageInfo&, void*, size_t, const Options&, SkPMColor*, int*, int*)
             override;
     SkEncodedFormat onGetEncodedFormat() const override { return kPNG_SkEncodedFormat; }
     bool onRewind() override;
-    uint32_t onGetFillValue(SkColorType) const override;
+    uint64_t onGetFillValue(const SkImageInfo&) const override;
 
     // Helper to set up swizzler, color xforms, and color table. Also calls png_read_update_info.
     bool initializeXforms(const SkImageInfo& dstInfo, const Options&, SkPMColor* colorPtr,
                           int* colorCount);
     void initializeSwizzler(const SkImageInfo& dstInfo, const Options&);
     SkSampler* getSampler(bool createIfNecessary) override;
     void allocateStorage(const SkImageInfo& dstInfo);
     void applyXformRow(void* dst, const void* src, SkColorType, SkAlphaType, int width);
 
     virtual int readRows(const SkImageInfo& dstInfo, void* dst, size_t rowBytes, int count,
@@ skipping 31 matching lines @@
         kSwizzleColor_XformMode,
     };
 
     bool createColorTable(const SkImageInfo& dstInfo, int* ctableCount);
     void destroyReadStruct();
 
     XformMode fXformMode;
 
     typedef SkCodec INHERITED;
 };