Don't decode AND mask for an icon that already has alpha information

Source/platform/image-decoders/ico/ICOImageDecoder.h

 /*
  * Copyright (c) 2008, 2009, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 56 matching lines @@
 
     enum FileType {
         ICON = 1,
         CURSOR = 2,
     };
 
     struct IconDirectoryEntry {
         IntSize m_size;
         uint16_t m_bitCount;
         IntPoint m_hotSpot;
+        uint32_t m_imageSize;
         uint32_t m_imageOffset;
     };
 
     // Returns true if |a| is a preferable icon entry to |b|.
     // Larger sizes, or greater bitdepths at the same size, are preferable.
     static bool compareEntries(const IconDirectoryEntry& a, const IconDirectoryEntry& b);
 
     inline uint16_t readUint16(int offset) const
     {
         return BMPImageReader::readUint16(m_data.get(), m_decodedOffset + offset);
@@ skipping 60 matching lines @@
     PNGDecoders m_pngDecoders;
 
     // Valid only while a BMPImageReader is decoding, this holds the size
     // for the particular entry being decoded.
     IntSize m_frameSize;
 };
 
 } // namespace blink
 
 #endif