Silence PNG warnings from SkPngCodec.

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 32 matching lines @@
 
 ///////////////////////////////////////////////////////////////////////////////
 // Callback functions
 ///////////////////////////////////////////////////////////////////////////////
 
 static void sk_error_fn(png_structp png_ptr, png_const_charp msg) {
     SkCodecPrintf("------ png error %s\n", msg);
     longjmp(png_jmpbuf(png_ptr), 1);
 }
 
+void sk_warning_fn(png_structp, png_const_charp msg) {
+    SkCodecPrintf("----- png warning %s\n", msg);
+}
+
 static void sk_read_fn(png_structp png_ptr, png_bytep data,
                        png_size_t length) {
     SkStream* stream = static_cast<SkStream*>(png_get_io_ptr(png_ptr));
     const size_t bytes = stream->read(data, length);
     if (bytes != length) {
         // FIXME: We want to report the fact that the stream was truncated.
         // One way to do that might be to pass a enum to longjmp so setjmp can
         // specify the failure.
         png_error(png_ptr, "Read Error!");
     }
@@ skipping 129 matching lines @@
         return false;
     }
     if (png_sig_cmp((png_bytep) buf, (png_size_t)0, PNG_BYTES_TO_CHECK)) {
         return false;
     }
     return true;
 }
 
 SkCodec* SkPngCodec::NewFromStream(SkStream* stream) {
     // The image is known to be a PNG. Decode enough to know the SkImageInfo.
-    // FIXME: Allow silencing warnings.
     png_structp png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL,
-                                                 sk_error_fn, NULL);
+                                                 sk_error_fn, sk_warning_fn);
     if (!png_ptr) {
         return NULL;
     }
 
     AutoCleanPng autoClean(png_ptr);
 
     png_infop info_ptr = png_create_info_struct(png_ptr);
     if (info_ptr == NULL) {
         return NULL;
     }
@@ skipping 354 matching lines @@
 
     SkASSERT(fNumberPasses != INVALID_NUMBER_PASSES);
     if (fNumberPasses > 1) {
         // We cannot efficiently do scanline decoding.
         return NULL;
     }
 
     return SkNEW_ARGS(SkPngScanlineDecoder, (dstInfo, this));
 }