Fix for events not firing on sanitized elements

tools/dom/templates/html/impl/impl_Element.darttemplate

Index: tools/dom/templates/html/impl/impl_Element.darttemplate
diff --git a/tools/dom/templates/html/impl/impl_Element.darttemplate b/tools/dom/templates/html/impl/impl_Element.darttemplate
index d258a6199c479f444bc03b098285927c9fc27d6b..6767a9e67e5b92c5820d510cc8c5df4ac5355ef9 100644
--- a/tools/dom/templates/html/impl/impl_Element.darttemplate
+++ b/tools/dom/templates/html/impl/impl_Element.darttemplate
@@ -584,7 +584,7 @@ $(ANNOTATIONS)abstract class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
   ElementList querySelectorAll(String selectors) =>
     new _FrozenElementList._wrap(_querySelectorAll(selectors));
 
-  /** 
+  /**
    * Alias for [querySelector]. Note this function is deprecated because its
    * semantics will be changing in the future.
    */
@@ -593,7 +593,7 @@ $(ANNOTATIONS)abstract class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
   @Experimental()
   Element query(String relativeSelectors) => querySelector(relativeSelectors);
 
-  /** 
+  /**
    * Alias for [querySelectorAll]. Note this function is deprecated because its
    * semantics will be changing in the future.
    */
@@ -1329,6 +1329,9 @@ $endif
     }
 
     treeSanitizer.sanitizeTree(fragment);
+    // Copy the fragment over to the main document (fix for 14184)
+    document.adoptNode(fragment);
+
     return fragment;
   }