Use signature inheritance when method types are unchanged

lib/src/codegen/js_codegen.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library dev_compiler.src.codegen.js_codegen;
 
 import 'dart:collection' show HashSet, HashMap;
 
 import 'package:analyzer/analyzer.dart' hide ConstantEvaluator;
 import 'package:analyzer/src/generated/ast.dart' hide ConstantEvaluator;
@@ skipping 574 matching lines @@
     // Emit the signature on the class recording the runtime type information
     {
       var tStatics = [];
       var tMethods = [];
       var sNames = [];
       var cType = classElem.type;
       for (MethodDeclaration node in methods) {
         if (!(node.isSetter || node.isGetter || node.isAbstract)) {
           var name = node.name.name;
           var element = node.element;
+          var inheritedElement =
+              classElem.lookUpInheritedConcreteMethod(name, currentLibrary);
+          if (inheritedElement != null &&
+              inheritedElement.type == element.type) continue;
           var unary = node.parameters.parameters.isEmpty;
           var memberName = _emitMemberName(name,
               type: cType, unary: unary, isStatic: node.isStatic);
           var property =
               new JS.Property(memberName, _emitTypeName(element.type));
           if (node.isStatic) {
             tStatics.add(property);
             sNames.add(memberName);
           } else tMethods.add(property);
         }
@@ skipping 1971 matching lines @@
 
 /// A special kind of element created by the compiler, signifying a temporary
 /// variable. These objects use instance equality, and should be shared
 /// everywhere in the tree where they are treated as the same variable.
 class TemporaryVariableElement extends LocalVariableElementImpl {
   TemporaryVariableElement.forNode(Identifier name) : super.forNode(name);
 
   int get hashCode => identityHashCode(this);
   bool operator ==(Object other) => identical(this, other);
 }