Implement CSS luminance masking using skia SkLumaMaskXfermode class.

Source/core/platform/graphics/skia/NativeImageSkia.cpp

Index: Source/core/platform/graphics/skia/NativeImageSkia.cpp
diff --git a/Source/core/platform/graphics/skia/NativeImageSkia.cpp b/Source/core/platform/graphics/skia/NativeImageSkia.cpp
index f43c4833b9eaef96689084b5619bda1d67bd30f7..9f774f1ec916ac34131d01dd9217fcea9c0313e5 100644
--- a/Source/core/platform/graphics/skia/NativeImageSkia.cpp
+++ b/Source/core/platform/graphics/skia/NativeImageSkia.cpp
@@ -45,6 +45,7 @@
 #include "third_party/skia/include/core/SkPaint.h"
 #include "third_party/skia/include/core/SkScalar.h"
 #include "third_party/skia/include/core/SkShader.h"
+#include "third_party/skia/include/effects/SkLumaXfermode.h"
 
 #include <limits>
 #include <math.h>
@@ -324,7 +325,11 @@ void NativeImageSkia::draw(GraphicsContext* context, const SkRect& srcRect, cons
 {
     TRACE_EVENT0("skia", "NativeImageSkia::draw");
     SkPaint paint;
-    paint.setXfermode(compOp.get());
+    if (context->drawLuminanceMask()) {

[eseidel, 2013/09/19 15:10:37]

I believe blink style says {} are avoided when there is only one line in the
clause.

+        paint.setXfermode(SkLumaMaskXfermode::Create(SkXfermode::kSrcOver_Mode));
+    } else {
+        paint.setXfermode(compOp.get());
+    }
     paint.setAlpha(context->getNormalizedAlpha());
     paint.setLooper(context->drawLooper());
     // only antialias if we're rotated or skewed
@@ -461,7 +466,11 @@ void NativeImageSkia::drawPattern(
 
     SkPaint paint;
     paint.setShader(shader.get());
-    paint.setXfermode(WebCoreCompositeToSkiaComposite(compositeOp, blendMode).get());
+    if (context->drawLuminanceMask()) {
+        paint.setXfermode(SkLumaMaskXfermode::Create(SkXfermode::kSrcOver_Mode));
+    } else {
+        paint.setXfermode(WebCoreCompositeToSkiaComposite(compositeOp, blendMode).get());
+    }
 
     paint.setFilterBitmap(resampling == LinearResampling);
     if (useBicubicFilter)