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

Source/core/platform/graphics/Color.h

 /*
  * Copyright (C) 2003, 2004, 2005, 2006, 2010 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 85 matching lines @@
     int blue() const { return blueChannel(m_color); }
     int alpha() const { return alphaChannel(m_color); }
     
     RGBA32 rgb() const { return m_color; } // Preserve the alpha.
     void setRGB(int r, int g, int b) { m_color = makeRGB(r, g, b); m_valid = true; }
     void setRGB(RGBA32 rgb) { m_color = rgb; m_valid = true; }
     void getRGBA(float& r, float& g, float& b, float& a) const;
     void getRGBA(double& r, double& g, double& b, double& a) const;
     void getHSL(double& h, double& s, double& l) const;
 
+    double lightness() const;
+
     Color light() const;
     Color dark() const;
 
     // This is an implementation of Porter-Duff's "source-over" equation
     Color blend(const Color&) const;
     Color blendWithWhite() const;
 
     static bool parseHexColor(const String&, RGBA32&);
     static bool parseHexColor(const LChar*, unsigned, RGBA32&);
     static bool parseHexColor(const UChar*, unsigned, RGBA32&);
@@ skipping 44 matching lines @@
     }
 
     return Color(blend(from.red(), to.red(), progress),
                  blend(from.green(), to.green(), progress),
                  blend(from.blue(), to.blue(), progress),
                  blend(from.alpha(), to.alpha(), progress));
 }
 } // namespace WebCore
 
 #endif // Color_h