Change the caret color according to the lightness of the background color.

Source/core/platform/graphics/Color.cpp

 /*
  * Copyright (C) 2003, 2004, 2005, 2006, 2008 Apple 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 396 matching lines @@
 
     lightness = 0.5 * (max + min);
     if (max == min)
         saturation = 0.0;
     else if (lightness <= 0.5)
         saturation = ((max - min) / (max + min));
     else
         saturation = ((max - min) / (2.0 - (max + min)));
 }
 
+double Color::lightness() const
+{
+    double hue, saturation, lightness;
+    getHSL(hue, saturation, lightness);
+
+    return lightness;
+}
+
 Color colorFromPremultipliedARGB(RGBA32 pixelColor)
 {
     int alpha = alphaChannel(pixelColor);
     if (alpha && alpha < 255) {
         return Color::createUnchecked(
             redChannel(pixelColor) * 255 / alpha,
             greenChannel(pixelColor) * 255 / alpha,
             blueChannel(pixelColor) * 255 / alpha,
             alpha);
     } else
@@ skipping 11 matching lines @@
             (color.green() * alpha  + 254) / 255,
             (color.blue() * alpha  + 254) / 255,
             alpha).rgb();
     } else
          pixelColor = color.rgb();
 
     return pixelColor;
 }
 
 } // namespace WebCore