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 67de9daf9ffd97666eb8c19c3f53b62c80fb7cec..24c1ec7acaba9c9607a7eec42322784ca90a75d9 100644
--- a/tests/html/html.status
+++ b/tests/html/html.status
@@ -9,6 +9,9 @@ webgl_1_test: Skip  # Issue 1495
 xmldocument_test: Skip  # XML in dart:html is incomplete
 xmlelement_test: Skip  # XML in dart:html is incomplete
 
+[ $runtime == chrome ]
+contentelement_test: Fail   # Issue 5445: not currently supported on chrome stable.
+
 [ $runtime == drt ]
 xhr_cross_origin_test: Skip  # Issue 4502: Passes with --allow-external-pages.
 
@@ -52,6 +55,7 @@ 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.
@@ -117,6 +121,7 @@ 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