Implement CSS luminance masking using skia SkLumaMaskXfermode class.

Source/core/platform/graphics/GraphicsContext.h

 /*
  * Copyright (C) 2003, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2008-2009 Torch Mobile, Inc.
  * 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 146 matching lines @@
 
     void setAlpha(float alpha) { m_state->m_alpha = alpha; }
 
     void setImageInterpolationQuality(InterpolationQuality quality) { m_state->m_interpolationQuality = quality; }
     InterpolationQuality imageInterpolationQuality() const { return m_state->m_interpolationQuality; }
 
     void setCompositeOperation(CompositeOperator, BlendMode = BlendModeNormal);
     CompositeOperator compositeOperation() const { return m_state->m_compositeOperator; }
     BlendMode blendModeOperation() const { return m_state->m_blendMode; }
 
+    void setDrawLuminanceMask(bool drawLuminanceMask) { m_state->m_drawLuminanceMask = drawLuminanceMask; }
+    bool drawLuminanceMask() const { return m_state->m_drawLuminanceMask; }
+
     // Change the way document markers are rendered.
     // Any deviceScaleFactor higher than 1.5 is enough to justify setting this flag.
     void setUseHighResMarkers(bool isHighRes) { m_useHighResMarker = isHighRes; }
 
     // If true we are (most likely) rendering to a web page and the
     // canvas has been prepared with an opaque background. If false,
     // the canvas may havbe transparency (as is the case when rendering
     // to a canvas object).
     void setCertainlyOpaque(bool isOpaque) { m_isCertainlyOpaque = isOpaque; }
     bool isCertainlyOpaque() const { return m_isCertainlyOpaque; }
@@ skipping 290 matching lines @@
     // FIXME: Make this go away: crbug.com/236892
     bool m_updatingControlTints : 1;
     bool m_accelerated : 1;
     bool m_isCertainlyOpaque : 1;
     bool m_printing : 1;
 };
 
 } // namespace WebCore
 
 #endif // GraphicsContext_h