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

Source/core/platform/graphics/ShadowBlur.cpp

 /*
  * Copyright (C) 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Sencha, Inc. All rights reserved.
  * Copyright (C) 2010 Igalia S.L. All rights reserved.
  * Copyright (C) Research In Motion Limited 2011. 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
@@ skipping 37 matching lines @@
 {
     updateShadowBlurValues();
 }
 
 void ShadowBlur::updateShadowBlurValues()
 {
     // Limit blur radius to 128 to avoid lots of very expensive blurring.
     m_blurRadius = m_blurRadius.shrunkTo(FloatSize(128, 128));
 
     // The type of shadow is decided by the blur radius, shadow offset, and shadow color.
-    if (!m_color.alpha()) {
+    if (!m_color.isValid() || !m_color.alpha()) {
         // Can't paint the shadow with invalid or invisible color.
         m_type = NoShadow;
     } else if (m_blurRadius.width() > 0 || m_blurRadius.height() > 0) {
         // Shadow is always blurred, even the offset is zero.
         m_type = BlurShadow;
     } else if (!m_offset.width() && !m_offset.height()) {
         // Without blur and zero offset means the shadow is fully hidden.
         m_type = NoShadow;
     } else
         m_type = SolidShadow;
@@ skipping 119 matching lines @@
 
         if (!m_blurRadius.height())
             break;
 
         if (m_blurRadius.width() != m_blurRadius.height())
             calculateLobes(lobes, m_blurRadius.height(), m_shadowsIgnoreTransforms);
     }
 }
 
 } // namespace WebCore