Reenable warnings in src/codec

src/codec/SkCodec_libpng.cpp

 /*
  * 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_libpng.h"
 #include "SkCodecPriv.h"
 #include "SkColorPriv.h"
@@ skipping 269 matching lines @@
     if (bitDepth < 8) {
         png_set_packing(png_ptr);
     }
 #endif
     // Expand grayscale images to the full 8 bits from 1, 2, or 4 bits/pixel.
     if (colorType == PNG_COLOR_TYPE_GRAY && bitDepth < 8) {
         png_set_expand_gray_1_2_4_to_8(png_ptr);
     }
 
     // Now determine the default SkColorType and SkAlphaType and set required transforms
-    SkColorType skColorType;
-    SkAlphaType skAlphaType;
+    SkColorType skColorType = kUnknown_SkColorType;
+    SkAlphaType skAlphaType = kUnknown_SkAlphaType;
     switch (colorType) {
         case PNG_COLOR_TYPE_PALETTE:
             skColorType = kIndex_8_SkColorType;
             skAlphaType = has_transparency_in_tRNS(png_ptr, info_ptr) ?
                     kUnpremul_SkAlphaType : kOpaque_SkAlphaType;
             break;
         case PNG_COLOR_TYPE_RGB:
             if (has_transparency_in_tRNS(png_ptr, info_ptr)) {
                 //convert to RGBA with tranparency information in tRNS chunk if it exists
                 png_set_tRNS_to_alpha(png_ptr);
@@ skipping 296 matching lines @@
     SkASSERT(false);
     return true;
 }
 
 // Subclass of SkPngCodec which supports scanline decoding
 class SkPngScanlineDecoder : public SkPngCodec {
 public:
     SkPngScanlineDecoder(const SkImageInfo& srcInfo, SkStream* stream,
             png_structp png_ptr, png_infop info_ptr, int bitDepth)
         : INHERITED(srcInfo, stream, png_ptr, info_ptr, bitDepth, 1)
+        , fAlphaState(kUnknown_AlphaState)
         , fSrcRow(nullptr)
-        , fAlphaState(kUnknown_AlphaState)
     {}
 
     Result onStartScanlineDecode(const SkImageInfo& dstInfo, const Options& options,
             SkPMColor ctable[], int* ctableCount) override {
         if (!conversion_possible(dstInfo, this->getInfo())) {
             return kInvalidConversion;
         }
 
         const Result result = this->initializeSwizzler(dstInfo, options, ctable,
                                                        ctableCount);
@@ skipping 216 matching lines @@
     }
 
     if (1 == numberPasses) {
         return new SkPngScanlineDecoder(imageInfo, streamDeleter.detach(), png_ptr, info_ptr,
                                         bitDepth);
     }
 
     return new SkPngInterlacedScanlineDecoder(imageInfo, streamDeleter.detach(), png_ptr,
                                               info_ptr, bitDepth, numberPasses);
 }
-