Adding constructor to ContentElement.

tests/html/html.status

Index: tests/html/html.status
diff --git a/tests/html/html.status b/tests/html/html.status
index 73f3863430975b09ec14bb0587833648fc8f4dab..cd663eb7cf6e39f76309588d2eca8740bdf11b75 100644
--- a/tests/html/html.status
+++ b/tests/html/html.status
@@ -53,6 +53,7 @@ unknownelement_test: Fail # Issue 4189
 history_test: Fail
 
 [ $runtime == ie ]
+contentelement_test: Fail   # ie does not support content element.
 form_data_test: Fail # Issue 4793.
 form_element_test: Fail # Issue 4793.
 typed_arrays_1_test: Skip   # ie9 does not have typed arrays.
@@ -119,6 +120,7 @@ css_test: Fail               # No analog to WebKitCSSMatrix
 callbacks_test: Fail         # (webkit|moz|ms)RequestAnimationFrame
 canvas_test: Fail            # No setFillColor() method.  Use fillstyle attribute instead.
 canvas_using_html_test: Fail # No setFillColor() method.  Use fillstyle attribute instead.
+contentelement_test: Fail    # FF does not support content element.
 dart_object_local_storage_test: Skip  # sessionStorage NS_ERROR_DOM_NOT_SUPPORTED_ERR
 documentfragment_test: Fail
 element_test: Fail