Replace static_cast with safe casting methods

Source/core/editing/EditorCommand.cpp

 /*
  * Copyright (C) 2006, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2009 Igalia S.L.
  *
  * 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.
@@ skipping 123 matching lines @@
 //        until https://bugs.webkit.org/show_bug.cgi?id=27818 is resolved.
 static bool executeToggleStyleInList(Frame* frame, EditorCommandSource source, EditAction action, CSSPropertyID propertyID, CSSValue* value)
 {
     RefPtr<EditingStyle> selectionStyle = EditingStyle::styleAtSelectionStart(frame->selection()->selection());
     if (!selectionStyle || !selectionStyle->style())
         return false;
 
     RefPtr<CSSValue> selectedCSSValue = selectionStyle->style()->getPropertyCSSValue(propertyID);
     String newStyle = ASCIILiteral("none");
     if (selectedCSSValue->isValueList()) {
-        RefPtr<CSSValueList> selectedCSSValueList = static_cast<CSSValueList*>(selectedCSSValue.get());
+        RefPtr<CSSValueList> selectedCSSValueList = toCSSValueList(selectedCSSValue.get());
         if (!selectedCSSValueList->removeAll(value))
             selectedCSSValueList->append(value);
         if (selectedCSSValueList->length())
             newStyle = selectedCSSValueList->cssText();
 
     } else if (selectedCSSValue->cssText() == "none")
         newStyle = value->cssText();
 
     // FIXME: We shouldn't be having to convert new style into text.  We should have setPropertyCSSValue.
     RefPtr<MutableStylePropertySet> newMutableStyle = MutableStylePropertySet::create();
@@ skipping 1587 matching lines @@
         return m_command->state(m_frame.get(), triggeringEvent) == TrueTriState ? "true" : "false";
     return m_command->value(m_frame.get(), triggeringEvent);
 }
 
 bool Editor::Command::isTextInsertion() const
 {
     return m_command && m_command->isTextInsertion;
 }
 
 } // namespace WebCore