Revert r154797: "Move isValid/isCurrentColor from Color to StyleColor"

Source/core/platform/graphics/DrawLooper.cpp

 /*
  * 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
@@ skipping 44 matching lines @@
 void DrawLooper::addUnmodifiedContent()
 {
     SkLayerDrawLooper::LayerInfo info;
     m_skDrawLooper->addLayerOnTop(info);
 }
 
 void DrawLooper::addShadow(const FloatSize& offset, float blur, const Color& color,
     ShadowTransformMode shadowTransformMode, ShadowAlphaMode shadowAlphaMode)
 {
     // Detect when there's no effective shadow.
-    if (!color.alpha())
+    if (!color.isValid() || !color.alpha())
         return;
 
-    SkColor skColor = color.rgb();
+    SkColor skColor;
+    if (color.isValid())
+        skColor = color.rgb();
+    else
+        skColor = SkColorSetARGB(0xFF / 3, 0, 0, 0); // "std" apple shadow color.
 
     SkLayerDrawLooper::LayerInfo info;
 
     switch (shadowAlphaMode) {
     case ShadowRespectsAlpha:
         info.fColorMode = SkXfermode::kDst_Mode;
         break;
     case ShadowIgnoresAlpha:
         info.fColorMode = SkXfermode::kSrc_Mode;
         break;
@@ skipping 16 matching lines @@
         RefPtr<SkMaskFilter> mf = adoptRef(SkBlurMaskFilter::Create(
             (double)blur / 2.0, SkBlurMaskFilter::kNormal_BlurStyle, mfFlags));
         paint->setMaskFilter(mf.get());
     }
 
     RefPtr<SkColorFilter> cf = adoptRef(SkColorFilter::CreateModeFilter(skColor, SkXfermode::kSrcIn_Mode));
     paint->setColorFilter(cf.get());
 }
 
 } // namespace WebCore