Move isValid/isCurrentColor from Color to StyleColor

Source/core/platform/graphics/DrawLooper.cpp

Index: Source/core/platform/graphics/DrawLooper.cpp
diff --git a/Source/core/platform/graphics/DrawLooper.cpp b/Source/core/platform/graphics/DrawLooper.cpp
index a1425c6f645cd30b05d2904b423090f99b503209..ef906ae10c1a01e05e7380cbfc64e5129505cdbf 100644
--- a/Source/core/platform/graphics/DrawLooper.cpp
+++ b/Source/core/platform/graphics/DrawLooper.cpp
@@ -53,14 +53,10 @@ void DrawLooper::addShadow(const FloatSize& offset, float blur, const Color& col
     ShadowTransformMode shadowTransformMode, ShadowAlphaMode shadowAlphaMode)
 {
     // Detect when there's no effective shadow.
-    if (!color.isValid() || !color.alpha())
+    if (!color.alpha())
         return;
 
-    SkColor skColor;
-    if (color.isValid())
-        skColor = color.rgb();
-    else
-        skColor = SkColorSetARGB(0xFF / 3, 0, 0, 0); // "std" apple shadow color.
+    SkColor skColor = color.rgb();
 
     SkLayerDrawLooper::LayerInfo info;