Use signature inheritance when method types are unchanged

test/codegen/expect/sunflower/dom.js

Index: test/codegen/expect/sunflower/dom.js
diff --git a/test/codegen/expect/sunflower/dom.js b/test/codegen/expect/sunflower/dom.js
index cf5520218b409e8370a012f07be5d198f5cb5c4c..4cf8d2f333e4dd419218d7a9d0d239731ad3d299 100644
--- a/test/codegen/expect/sunflower/dom.js
+++ b/test/codegen/expect/sunflower/dom.js
@@ -8,20 +8,16 @@ var core = dart.import(core);
       this.name = name;
     }
   }
-  dart.setSignature(JsName, {});
   class Overload extends core.Object {
     Overload() {
     }
   }
-  dart.setSignature(Overload, {});
   let overload = dart.const(new Overload());
   let EventListener = dart.typedef('EventListener', () => dart.functionType(dart.void, [Event]));
   class Event extends core.Object {}
-  dart.setSignature(Event, {});
   let InputElement = HTMLInputElement;
   let CanvasElement = HTMLCanvasElement;
   class RenderingContext extends core.Object {}
-  dart.setSignature(RenderingContext, {});
   class CanvasDrawingStyles extends core.Object {
     CanvasDrawingStyles() {
       this.lineWidth = null;
@@ -34,9 +30,7 @@ var core = dart.import(core);
       this.textBaseline = null;
     }
   }
-  dart.setSignature(CanvasDrawingStyles, {});
   class CanvasPathMethods extends core.Object {}
-  dart.setSignature(CanvasPathMethods, {});
   // Exports:
   exports.JsName = JsName;
   exports.Overload = Overload;