Merging dart:html interfaces and implementations

lib/html/templates/html/impl/impl_CustomEvent.darttemplate

Index: lib/html/templates/html/impl/impl_CustomEvent.darttemplate
diff --git a/lib/html/templates/html/impl/impl_ShadowRoot.darttemplate b/lib/html/templates/html/impl/impl_CustomEvent.darttemplate
similarity index 61%
copy from lib/html/templates/html/impl/impl_ShadowRoot.darttemplate
copy to lib/html/templates/html/impl/impl_CustomEvent.darttemplate
index 32c953a0f895e91db3676c694d43d22f36f01170..8d20b9d0dd123c573c93b584e834b0d5a556cc7e 100644
--- a/lib/html/templates/html/impl/impl_ShadowRoot.darttemplate
+++ b/lib/html/templates/html/impl/impl_CustomEvent.darttemplate
@@ -5,11 +5,8 @@
 // WARNING: Do not edit - generated code.
 
 class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
+  factory $CLASSNAME(String type, [bool canBubble = true, bool cancelable = true,
+      Object detail = null]) => _$(CLASSNAME)FactoryProvider.create$CLASSNAME(
+      type, canBubble, cancelable, detail);
 $!MEMBERS
-$if DART2JS
-  static bool get supported =>
-      JS('bool', '!!(window.ShadowRoot || window.WebKitShadowRoot)');
-$else
-  static bool get supported => _Utils.shadowRootSupported(window.document);
-$endif
 }