Add toSVGColor|Paint() to cleanup static_cast<>, and use it

Source/core/svg/SVGPaint.h

Index: Source/core/svg/SVGPaint.h
diff --git a/Source/core/svg/SVGPaint.h b/Source/core/svg/SVGPaint.h
index f4f387dde152f64b63ffb32572d4ab58be031c92..9d6379be521004414ebed00aa1c0e6231f9a2a5c 100644
--- a/Source/core/svg/SVGPaint.h
+++ b/Source/core/svg/SVGPaint.h
@@ -116,6 +116,21 @@ private:
     String m_uri;
 };
 
+// This will catch anyone doing an unnecessary cast.
+SVGPaint* toSVGPaint(const SVGColor*);
+
+inline SVGPaint* toSVGPaint(CSSValue* value)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!value || value->isSVGPaint());
+    return static_cast<SVGPaint*>(value);
+}
+
+inline const SVGPaint* toSVGPaint(const CSSValue* value)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!value || value->isSVGPaint());
+    return static_cast<const SVGPaint*>(value);
+}
+
 } // namespace WebCore
 
 #endif // SVGPaint_h