Make image decoders faster by refactoring hot loops that fills the lines of ImageFrame.

Source/core/platform/image-decoders/webp/WEBPImageDecoder.cpp

 /*
  * Copyright (C) 2010 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:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 176 matching lines @@
     }
 
     ASSERT(width == size().width());
     ASSERT(decodedHeight <= size().height());
 
     for (int y = m_decodedHeight; y < decodedHeight; ++y) {
         uint8_t* row = reinterpret_cast<uint8_t*>(buffer.getAddr(0, y));
         if (qcms_transform* transform = colorTransform())
             qcms_transform_data_type(transform, row, row, width, QCMS_OUTPUT_RGBX);
         uint8_t* pixel = row;
-        for (int x = 0; x < width; ++x, pixel += 4)
-            buffer.setRGBA(x, y, pixel[0], pixel[1], pixel[2], pixel[3]);
+
+        // Do not merge the loops below. They are hand rolled for each case for maximal peformace.
+        ImageFrame::PixelData* dst = buffer.getAddr(0, y);
+        if (buffer.premultiplyAlpha()) {
+            for (int x = 0; x < width; ++x, pixel += 4)
+                buffer.setRGBAPremultiply(dst + x, pixel[0], pixel[1], pixel[2], pixel[3]);
+        } else {
+            for (int x = 0; x < width; ++x, pixel += 4)
+                buffer.setRGBANoPremultiply(dst + x, pixel[0], pixel[1], pixel[2], pixel[3]);
+        }
     }
 
     m_decodedHeight = decodedHeight;
 }
 
 #endif // QCMS_WEBP_COLOR_CORRECTION
 
 bool WEBPImageDecoder::decode(bool onlySize)
 {
     if (failed())
@@ skipping 83 matching lines @@
         if ((m_formatFlags & ICCP_FLAG) && !ignoresGammaAndColorProfile()) 
             applyColorProfile(dataBytes, dataSize, buffer);
         return false;
     default:
         clear();                         
         return setFailed();
     }
 }
 
 } // namespace WebCore