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

Source/core/platform/graphics/GraphicsLayer.cpp

 /*
  * Copyright (C) 2009 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 746 matching lines @@
     if (flags & LayerTreeIncludesDebugInfo) {
         writeIndent(ts, indent + 1);
         ts << "(";
         if (m_client)
             ts << "client " << static_cast<void*>(m_client);
         else
             ts << "no client";
         ts << ")\n";
     }
 
-    if (m_backgroundColor != Color::transparent) {
+    if (m_backgroundColor.isValid() && m_backgroundColor != Color::transparent) {
         writeIndent(ts, indent + 1);
         ts << "(backgroundColor " << m_backgroundColor.nameForRenderTreeAsText() << ")\n";
     }
 
     if (!m_transform.isIdentity()) {
         writeIndent(ts, indent + 1);
         ts << "(transform ";
         ts << "[" << m_transform.m11() << " " << m_transform.m12() << " " << m_transform.m13() << " " << m_transform.m14() << "] ";
         ts << "[" << m_transform.m21() << " " << m_transform.m22() << " " << m_transform.m23() << " " << m_transform.m24() << "] ";
         ts << "[" << m_transform.m31() << " " << m_transform.m32() << " " << m_transform.m33() << " " << m_transform.m34() << "] ";
@@ skipping 552 matching lines @@
 #ifndef NDEBUG
 void showGraphicsLayerTree(const WebCore::GraphicsLayer* layer)
 {
     if (!layer)
         return;
 
     String output = layer->layerTreeAsText(WebCore::LayerTreeIncludesDebugInfo);
     fprintf(stderr, "%s\n", output.utf8().data());
 }
 #endif