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

Source/core/page/FrameView.h

Index: Source/core/page/FrameView.h
diff --git a/Source/core/page/FrameView.h b/Source/core/page/FrameView.h
index e89dba444d65c6fb9179e00b82e9532687bd3d0c..8183a9b5875b349a4bb784648a23657f248df88f 100644
--- a/Source/core/page/FrameView.h
+++ b/Source/core/page/FrameView.h
@@ -137,8 +137,8 @@ public:
     bool hasOpaqueBackground() const;
 
     Color baseBackgroundColor() const;
-    void setBaseBackgroundColor(const StyleColor&);
-    void updateBackgroundRecursively(const StyleColor&, bool);
+    void setBaseBackgroundColor(const Color&);
+    void updateBackgroundRecursively(const Color&, bool);
 
     bool shouldUpdateWhileOffscreen() const;
     void setShouldUpdateWhileOffscreen(bool);
@@ -229,7 +229,7 @@ public:
     virtual void paintScrollCorner(GraphicsContext*, const IntRect& cornerRect);
     virtual void paintScrollbar(GraphicsContext*, Scrollbar*, const IntRect&) OVERRIDE;
 
-    StyleColor documentBackgroundColor() const;
+    Color documentBackgroundColor() const;
 
     static double currentFrameTimeStamp() { return s_currentFrameTimeStamp; }