Add canvas blending modes under a runtime flag

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

Index: Source/core/platform/graphics/skia/SkiaUtils.cpp
diff --git a/Source/core/platform/graphics/skia/SkiaUtils.cpp b/Source/core/platform/graphics/skia/SkiaUtils.cpp
index 9b343ff8b3501b55736714ae33665e5aae30ecb3..cc9c0095e769d430ae7efbd0c81f6e26b9e3944a 100644
--- a/Source/core/platform/graphics/skia/SkiaUtils.cpp
+++ b/Source/core/platform/graphics/skia/SkiaUtils.cpp
@@ -61,8 +61,53 @@ static const struct CompositOpToXfermodeMode {
     { CompositePlusLighter,     SkXfermode::kPlus_Mode }
 };
 
-SkXfermode::Mode WebCoreCompositeToSkiaComposite(CompositeOperator op)
+COMPILE_ASSERT((BlendModeNormal == 0
+                && BlendModeMultiply == 1
+                && BlendModeScreen == 2
+                && BlendModeOverlay == 3
+                && BlendModeDarken == 4
+                && BlendModeLighten == 5
+                && BlendModeColorDodge == 6
+                && BlendModeColorBurn == 7
+                && BlendModeHardLight == 8
+                && BlendModeSoftLight == 9
+                && BlendModeDifference == 10
+                && BlendModeExclusion == 11
+                && BlendModeHue == 12
+                && BlendModeSaturation == 13
+                && BlendModeColor == 14
+                && BlendModeLuminosity == 15),
+    KeepBlendOpsAndSkXfermodesInSync);
+
+static const uint8_t gMapBlendOpsToXfermodeModes[] = {
+    SkXfermode::kClear_Mode, // BlendModeNormal
+    SkXfermode::kMultiply_Mode, // BlendModeMultiply
+    SkXfermode::kScreen_Mode, // BlendModeScreen
+    SkXfermode::kOverlay_Mode, // BlendModeOverlay
+    SkXfermode::kDarken_Mode, // BlendModeDarken
+    SkXfermode::kLighten_Mode, // BlendModeLighten
+    SkXfermode::kColorDodge_Mode, // BlendModeColorDodge
+    SkXfermode::kColorBurn_Mode, // BlendModeColorBurn
+    SkXfermode::kHardLight_Mode, // BlendModeHardLight
+    SkXfermode::kSoftLight_Mode, // BlendModeSoftLight
+    SkXfermode::kDifference_Mode, // BlendModeDifference
+    SkXfermode::kExclusion_Mode, // BlendModeExclusion
+    SkXfermode::kHue_Mode, // BlendModeHue
+    SkXfermode::kSaturation_Mode, // BlendModeSaturation
+    SkXfermode::kColor_Mode, // BlendModeColor
+    SkXfermode::kLuminosity_Mode // BlendModeLuminosity
+};
+
+SkXfermode::Mode WebCoreCompositeToSkiaComposite(CompositeOperator op, BlendMode blendMode)
 {
+    if (blendMode != BlendModeNormal) {
+        if ((uint8_t)blendMode >= SK_ARRAY_COUNT(gMapBlendOpsToXfermodeModes)) {
+            SkDEBUGF(("GraphicsContext::setPlatformCompositeOperation unknown BlendMode %d\n", blendMode));
+            return SkXfermode::kSrcOver_Mode;
+        }
+        return (SkXfermode::Mode)gMapBlendOpsToXfermodeModes[(uint8_t)blendMode];
+    }
+
     const CompositOpToXfermodeMode* table = gMapCompositOpsToXfermodeModes;
     
     for (unsigned i = 0; i < SK_ARRAY_COUNT(gMapCompositOpsToXfermodeModes); i++) {