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

Source/core/html/track/TextTrackCueGeneric.h

Index: Source/core/html/track/TextTrackCueGeneric.h
diff --git a/Source/core/html/track/TextTrackCueGeneric.h b/Source/core/html/track/TextTrackCueGeneric.h
index 9034222841ec7f2f70b80ec490f4002bb6ed8756..a62611a07e5766bd4961b0078d4f226e59165249 100644
--- a/Source/core/html/track/TextTrackCueGeneric.h
+++ b/Source/core/html/track/TextTrackCueGeneric.h
@@ -61,10 +61,11 @@ public:
     void setFontName(String name) { m_fontName = name; }
 
     Color foregroundColor() const { return m_foregroundColor; }
-    void setForegroundColor(Color color) { m_foregroundColor = color; }
+
+    void setForegroundColor(RGBA32 color) { m_foregroundColor.setRGB(color); }
 
     Color backgroundColor() const { return m_backgroundColor; }
-    void setBackgroundColor(Color color) { m_backgroundColor = color; }
+    void setBackgroundColor(RGBA32 color) { m_backgroundColor.setRGB(color); }
 
     virtual void videoSizeDidChange(const IntSize&);