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

Source/core/html/track/TextTrackCueGeneric.cpp

 /*
  * Copyright (C) 2013 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 55 matching lines @@
     } else {
         setInlineStyleProperty(CSSPropertyLeft, static_cast<float>(cue->position()), CSSPrimitiveValue::CSS_PERCENTAGE);
         setInlineStyleProperty(CSSPropertyTop, static_cast<float>(cue->line()), CSSPrimitiveValue::CSS_PERCENTAGE);
 
         if (cue->getWritingDirection() == TextTrackCue::Horizontal)
             setInlineStyleProperty(CSSPropertyWidth, size, CSSPrimitiveValue::CSS_PERCENTAGE);
         else
             setInlineStyleProperty(CSSPropertyHeight, size,  CSSPrimitiveValue::CSS_PERCENTAGE);
     }
 
-    if (cue->foregroundColor().alpha())
+    if (cue->foregroundColor().isValid())
         setInlineStyleProperty(CSSPropertyColor, cue->foregroundColor().serialized());
 
-    if (cue->backgroundColor().alpha())
+    if (cue->backgroundColor().isValid())
         cue->element()->setInlineStyleProperty(CSSPropertyBackgroundColor, cue->backgroundColor().serialized());
 
     if (cue->getWritingDirection() == TextTrackCue::Horizontal)
         setInlineStyleProperty(CSSPropertyHeight, CSSValueAuto);
     else
         setInlineStyleProperty(CSSPropertyWidth, CSSValueAuto);
 
     if (cue->baseFontSizeRelativeToVideoHeight()) {
         double fontSize = videoSize.height() * cue->baseFontSizeRelativeToVideoHeight() / 100;
         if (cue->fontSizeMultiplier())
@@ skipping 69 matching lines @@
     if (m_foregroundColor != other->foregroundColor())
         return false;
     if (m_backgroundColor != other->backgroundColor())
         return false;
 
     return TextTrackCue::operator==(cue);
 }
 
 } // namespace WebCore