Replace static_cast with safe casting methods

Source/core/rendering/style/StylePendingImage.h

Index: Source/core/rendering/style/StylePendingImage.h
diff --git a/Source/core/rendering/style/StylePendingImage.h b/Source/core/rendering/style/StylePendingImage.h
index 9f7bc2afda544cebfb4518531805bdedc48e1a4f..38b59799408cc0e75cef92a309d08a6ff7b71713 100644
--- a/Source/core/rendering/style/StylePendingImage.h
+++ b/Source/core/rendering/style/StylePendingImage.h
@@ -43,10 +43,10 @@ class StylePendingImage : public StyleImage {
 public:
     static PassRefPtr<StylePendingImage> create(CSSValue* value) { return adoptRef(new StylePendingImage(value)); }
 
-    virtual WrappedImagePtr data() const { return static_cast<CSSImageValue*>(m_value); }
+    virtual WrappedImagePtr data() const { return toCSSImageValue(m_value); }
 
     virtual PassRefPtr<CSSValue> cssValue() const { return m_value; }
-    CSSImageValue* cssImageValue() const { return m_value->isImageValue() ? static_cast<CSSImageValue*>(m_value) : 0; }
+    CSSImageValue* cssImageValue() const { return m_value->isImageValue() ? toCSSImageValue(m_value) : 0; }
     CSSImageGeneratorValue* cssImageGeneratorValue() const { return m_value->isImageGeneratorValue() ? static_cast<CSSImageGeneratorValue*>(m_value) : 0; }
     CSSCursorImageValue* cssCursorImageValue() const { return m_value->isCursorImageValue() ? static_cast<CSSCursorImageValue*>(m_value) : 0; }
     CSSImageSetValue* cssImageSetValue() const { return m_value->isImageSetValue() ? static_cast<CSSImageSetValue*>(m_value) : 0; }