Cherry-pick WebKit security fix (webkit.org r68860) Do not merge

See http://trac.webkit.org/changeset/68860

Change-Id: I7860374528be836e1f4ea7c6faa48966fd3ed23c
diff --git a/WebCore/rendering/RenderObjectChildList.cpp b/WebCore/rendering/RenderObjectChildList.cpp
index 24e8645..65c35f0 100644
--- a/WebCore/rendering/RenderObjectChildList.cpp
+++ b/WebCore/rendering/RenderObjectChildList.cpp
@@ -429,7 +429,10 @@
                 generatedContentContainer->setStyle(pseudoElementStyle);
                 owner->addChild(generatedContentContainer, insertBefore);
             }
-            generatedContentContainer->addChild(renderer);
+            if (generatedContentContainer->isChildAllowed(renderer, pseudoElementStyle))
+                generatedContentContainer->addChild(renderer);
+            else
+                renderer->destroy();
         }
     }
 }