Implement CSS luminance masking using skia SkLumaMaskXfermode class.

Source/core/platform/graphics/GraphicsContextState.h

 // Copyright (C) 2013 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
 // copyright notice, this list of conditions and the following disclaimer
@@ skipping 47 matching lines @@
         , m_compositeOperator(CompositeSourceOver)
         , m_blendMode(BlendModeNormal)
 #if USE(LOW_QUALITY_IMAGE_INTERPOLATION)
         , m_interpolationQuality(InterpolationLow)
 #else
         , m_interpolationQuality(InterpolationHigh)
 #endif
         , m_shouldAntialias(true)
         , m_shouldSmoothFonts(true)
         , m_shouldClampToSourceRect(true)
+        , m_drawLuminanceMask(false)
     {
     }
 
     GraphicsContextState(const GraphicsContextState& other)
         : m_strokeData(other.m_strokeData)
         , m_fillColor(other.m_fillColor)
         , m_fillRule(other.m_fillRule)
         , m_fillGradient(other.m_fillGradient)
         , m_fillPattern(other.m_fillPattern)
         , m_looper(other.m_looper)
         , m_textDrawingMode(other.m_textDrawingMode)
         , m_alpha(other.m_alpha)
         , m_xferMode(other.m_xferMode)
         , m_colorFilter(other.m_colorFilter)
         , m_compositeOperator(other.m_compositeOperator)
         , m_blendMode(other.m_blendMode)
         , m_interpolationQuality(other.m_interpolationQuality)
         , m_shouldAntialias(other.m_shouldAntialias)
         , m_shouldSmoothFonts(other.m_shouldSmoothFonts)
         , m_shouldClampToSourceRect(other.m_shouldClampToSourceRect)
+        , m_drawLuminanceMask(other.m_drawLuminanceMask)
     {
     }
 
     // Helper function for applying the state's alpha value to the given input
     // color to produce a new output color.
     SkColor applyAlpha(SkColor c) const
     {
         int s = roundf(m_alpha * 256);
         if (s >= 256)
             return c;
@@ skipping 33 matching lines @@
     // Compositing control, for the CSS and Canvas compositing spec.
     CompositeOperator m_compositeOperator;
     BlendMode m_blendMode;
 
     // Image interpolation control.
     InterpolationQuality m_interpolationQuality;
 
     bool m_shouldAntialias : 1;
     bool m_shouldSmoothFonts : 1;
     bool m_shouldClampToSourceRect : 1;
+    bool m_drawLuminanceMask : 1;
 };
 
 } // namespace WebCore
 
 #endif // GraphicsContextState_h