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

Source/core/platform/image-decoders/jpeg/JPEGImageDecoder.cpp

Index: Source/core/platform/image-decoders/jpeg/JPEGImageDecoder.cpp
diff --git a/Source/core/platform/image-decoders/jpeg/JPEGImageDecoder.cpp b/Source/core/platform/image-decoders/jpeg/JPEGImageDecoder.cpp
index 7974b79a7ee2dd3a4fbb4c7579bab8dad2315872..cc2b43bda198021fc04cc63296919b11c8df7e47 100644
--- a/Source/core/platform/image-decoders/jpeg/JPEGImageDecoder.cpp
+++ b/Source/core/platform/image-decoders/jpeg/JPEGImageDecoder.cpp
@@ -637,31 +637,7 @@ bool JPEGImageDecoder::setFailed()
     return ImageDecoder::setFailed();
 }
 
-template <J_COLOR_SPACE colorSpace> void setPixel(ImageFrame& buffer, ImageFrame::PixelData* pixel, JSAMPARRAY samples, int column)
-{
-    JSAMPLE* jsample = *samples + column * (colorSpace == JCS_RGB ? 3 : 4);
-
-    switch (colorSpace) {
-    case JCS_RGB:
-        buffer.setRGBA(pixel, jsample[0], jsample[1], jsample[2], 0xFF);
-        break;
-    case JCS_CMYK:
-        // Source is 'Inverted CMYK', output is RGB.
-        // See: http://www.easyrgb.com/math.php?MATH=M12#text12
-        // Or: http://www.ilkeratalay.com/colorspacesfaq.php#rgb
-        // From CMYK to CMY:
-        // X =   X    * (1 -   K   ) +   K  [for X = C, M, or Y]
-        // Thus, from Inverted CMYK to CMY is:
-        // X = (1-iX) * (1 - (1-iK)) + (1-iK) => 1 - iX*iK
-        // From CMY (0..1) to RGB (0..1):
-        // R = 1 - C => 1 - (1 - iC*iK) => iC*iK  [G and B similar]
-        unsigned k = jsample[3];
-        buffer.setRGBA(pixel, jsample[0] * k / 255, jsample[1] * k / 255, jsample[2] * k / 255, 0xFF);
-        break;
-    }
-}
-
-template <J_COLOR_SPACE colorSpace> bool outputRows(JPEGImageReader* reader, ImageFrame& buffer)
+static bool outputRows(JPEGImageReader* reader, ImageFrame& buffer, J_COLOR_SPACE colorSpace)
 {
     JSAMPARRAY samples = reader->samples();
     jpeg_decompress_struct* info = reader->info();
@@ -678,9 +654,13 @@ template <J_COLOR_SPACE colorSpace> bool outputRows(JPEGImageReader* reader, Ima
         if (reader->colorTransform() && colorSpace == JCS_RGB)
             qcms_transform_data(reader->colorTransform(), *samples, *samples, width);
 #endif
-        ImageFrame::PixelData* pixel = buffer.getAddr(0, y);
-        for (int x = 0; x < width; ++pixel, ++x)
-            setPixel<colorSpace>(buffer, pixel, samples, x);
+        unsigned const char* row = *samples;
+        if (colorSpace == JCS_RGB)
+            buffer.fillRowFromRGBSource(y, row);
+        else if (colorSpace == JCS_CMYK)
+            buffer.fillRowFromInvertedCMYK(y, row);
+        else
+            ASSERT_NOT_REACHED();
     }
 
     return true;
@@ -722,16 +702,7 @@ bool JPEGImageDecoder::outputScanlines()
      }
 #endif
 
-    switch (info->out_color_space) {
-    case JCS_RGB:
-        return outputRows<JCS_RGB>(m_reader.get(), buffer);
-    case JCS_CMYK:
-        return outputRows<JCS_CMYK>(m_reader.get(), buffer);
-    default:
-        ASSERT_NOT_REACHED();
-    }
-
-    return setFailed();
+    return outputRows(m_reader.get(), buffer, info->out_color_space);
 }
 
 void JPEGImageDecoder::jpegComplete()