Revert of Never consolidate data in ICO decoder

Source/platform/image-decoders/png/PNGImageDecoder.cpp

Index: Source/platform/image-decoders/png/PNGImageDecoder.cpp
diff --git a/Source/platform/image-decoders/png/PNGImageDecoder.cpp b/Source/platform/image-decoders/png/PNGImageDecoder.cpp
index fed773021f8a0a47147b266ff6131c80c1c48bb0..99fde2f278671211987446b4b73657c8e4f37586 100644
--- a/Source/platform/image-decoders/png/PNGImageDecoder.cpp
+++ b/Source/platform/image-decoders/png/PNGImageDecoder.cpp
@@ -89,9 +89,9 @@
 class PNGImageReader {
     WTF_MAKE_FAST_ALLOCATED(PNGImageReader);
 public:
-    PNGImageReader(PNGImageDecoder* decoder, unsigned readOffset)
+    PNGImageReader(PNGImageDecoder* decoder)
         : m_decoder(decoder)
-        , m_readOffset(readOffset)
+        , m_readOffset(0)
         , m_currentBufferSize(0)
         , m_decodingSizeOnly(false)
         , m_hasAlpha(false)
@@ -204,10 +204,9 @@
 #endif
 };
 
-PNGImageDecoder::PNGImageDecoder(AlphaOption alphaOption, GammaAndColorProfileOption colorOptions, size_t maxDecodedBytes, unsigned offset)
+PNGImageDecoder::PNGImageDecoder(AlphaOption alphaOption, GammaAndColorProfileOption colorOptions, size_t maxDecodedBytes)
     : ImageDecoder(alphaOption, colorOptions, maxDecodedBytes)
     , m_hasColorProfile(false)
-    , m_offset(offset)
 {
 }
 
@@ -496,7 +495,7 @@
         return;
 
     if (!m_reader)
-        m_reader = adoptPtr(new PNGImageReader(this, m_offset));
+        m_reader = adoptPtr(new PNGImageReader(this));
 
     // If we couldn't decode the image but have received all the data, decoding
     // has failed.