Refined types for most HtmlElement factory constructors

tools/dom/scripts/systemhtml.py

Index: tools/dom/scripts/systemhtml.py
diff --git a/tools/dom/scripts/systemhtml.py b/tools/dom/scripts/systemhtml.py
index 4fc7e6ef772e08d4c1f5fd78f8fcd090a2266f70..dc1d79e435d84c693f375725718513460de22b6e 100644
--- a/tools/dom/scripts/systemhtml.py
+++ b/tools/dom/scripts/systemhtml.py
@@ -463,6 +463,19 @@ js_support_checks = dict({
             else ElemSupportStr(_html_element_constructors[key])) for key in
     _js_support_checks_basic_element_with_constructors +
     _js_support_checks_additional_element).items())
+
+
+# JavaScript element class names of elements for which createElement does not
+# always return exactly the right element, either because it might not be
+# supported, or some browser does something weird.
+_js_unreliable_element_factories = set(
+    _js_support_checks_basic_element_with_constructors +
+    _js_support_checks_additional_element +
+    [
+        'HTMLEmbedElement',
+        'HTMLObjectElement',
+    ])
+
 # ------------------------------------------------------------------------------
 
 class HtmlDartInterfaceGenerator(object):
@@ -804,6 +817,26 @@ class Dart2JSBackend(HtmlDartGenerator):
     # Custom factory will be taken from the template.
     return self._interface.doc_js_name in _js_custom_constructors
 
+  def MakeFactoryCall(self, factory, method, arguments, constructor_info):
+    if factory is 'document' and method is 'createElement' \
+        and not ',' in arguments \
+        and not self._HasUnreliableFactoryConstructor():
+      return emitter.Format(
+          "JS('returns:$INTERFACE_NAME;creates:$INTERFACE_NAME;new:true',"
+          " '#.$METHOD(#)', $FACTORY, $ARGUMENTS)",
+          INTERFACE_NAME=self._interface_type_info.interface_name(),
+          FACTORY=factory,
+          METHOD=method,
+          ARGUMENTS=arguments)
+    return emitter.Format(
+        '$FACTORY.$METHOD($ARGUMENTS)',
+        FACTORY=factory,
+        METHOD=method,
+        ARGUMENTS=arguments)
+
+  def _HasUnreliableFactoryConstructor(self):
+    return self._interface.doc_js_name in _js_unreliable_element_factories
+
   def IsConstructorArgumentOptional(self, argument):
     return argument.optional