emit interfaces before use

lib/src/codegen/js_codegen.dart

Index: lib/src/codegen/js_codegen.dart
diff --git a/lib/src/codegen/js_codegen.dart b/lib/src/codegen/js_codegen.dart
index 5b016e261e5736e163d1242dd1862015d4007672..b89179016912e926b45b8ad6cef56fa4ba80aa8e 100644
--- a/lib/src/codegen/js_codegen.dart
+++ b/lib/src/codegen/js_codegen.dart
@@ -372,6 +372,9 @@ class JSCodegenVisitor extends GeneralizingAstVisitor with ConversionVisitor {
     for (var m in classElem.mixins) {
       _emitClassIfNeeded(classDefs, m.element);
     }
+    for (var i in classElem.interfaces) {
+      _emitClassIfNeeded(classDefs, i.element);
+    }
     classDefs.add(body);
     return _statement(classDefs);
   }
@@ -398,6 +401,10 @@ class JSCodegenVisitor extends GeneralizingAstVisitor with ConversionVisitor {
       if (result) break;
       result = _classMightNotBeLoaded(mixin.element);
     }
+    for (var iface in cls.interfaces) {
+      if (result) break;
+      result = _classMightNotBeLoaded(iface.element);
+    }
     return _lazyClassMemo[cls] = result;
   }