Warn about overriding operator== but not hashCode.

dart/tests/utils/dummy_compiler_test.dart

 // Copyright (c) 2012, 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.
 // VMOptions=
 // VMOptions=--print-object-histogram
 
 // Smoke test of the dart2js compiler API.
 library dummy_compiler;
 
 import 'dart:async';
 
 import '../../sdk/lib/_internal/compiler/compiler.dart';
 
 Future<String> provider(Uri uri) {
   String source;
   if (uri.scheme == "main") {
     source = "main() {}";
   } else if (uri.scheme == "lib") {
     if (uri.path.endsWith("/core.dart")) {
-      source = """library core;
-                  class Object {
-                    operator==(other) {}
-                  }
-                  class Type {}
-                  class bool {}
-                  class num {}
-                  class int {}
-                  class double{}
-                  class String{}
-                  class Function{}
-                  class List {}
-                  class Map {}
-                  class Closure {}
-                  class BoundClosure {}
-                  class Dynamic_ {}
-                  class Null {}
-                  class StackTrace {}
-                  class LinkedHashMap {}
-                  identical(a, b) => true;
-                  getRuntimeTypeInfo(o) {}
-                  setRuntimeTypeInfo(o, i) {}
-                  eqNull(a) {}
-                  eqNullB(a) {}""";
+      source = """
+library core;
+class Object {
+  operator==(other) {}
+  get hashCode => throw 'Object.hashCode not implemented.';
+}
+class Type {}
+class bool {}
+class num {}
+class int {}
+class double{}
+class String{}
+class Function{}
+class List {}
+class Map {}
+class Closure {}
+class BoundClosure {}
+class Dynamic_ {}
+class Null {}
+class StackTrace {}
+class LinkedHashMap {}
+identical(a, b) => true;
+getRuntimeTypeInfo(o) {}
+setRuntimeTypeInfo(o, i) {}
+eqNull(a) {}
+eqNullB(a) {}""";
     } else if (uri.path.endsWith('_patch.dart')) {
       source = '';
     } else if (uri.path.endsWith('interceptors.dart')) {
-      source = """class Interceptor {
-                    operator==(other) {}
-                  }
-                  class JSIndexable {
-                    get length;
-                  }
-                  class JSMutableIndexable {}
-                  class JSArray implements JSIndexable {
-                    var removeLast;
-                    var add;
-                  }
-                  class JSMutableArray extends JSArray {}
-                  class JSFixedArray extends JSMutableArray {}
-                  class JSExtendableArray extends JSMutableArray {}
-                  class JSString implements JSIndexable {
-                    var split;
-                    var concat;
-                    var toString;
-                  }
-                  class JSFunction {}
-                  class JSInt {}
-                  class JSDouble {}
-                  class JSNumber {}
-                  class JSNull {}
-                  class JSBool {}
-                  getInterceptor(o){}
-                  getDispatchProperty(o) {}
-                  setDispatchProperty(o, v) {}""";
+      source = """
+class Interceptor {
+  operator==(other) {}
+  get hashCode => throw 'Interceptor.hashCode not implemented.';
+}
+class JSIndexable {
+  get length;
+}
+class JSMutableIndexable {}
+class JSArray implements JSIndexable {
+  var removeLast;
+  var add;
+}
+class JSMutableArray extends JSArray {}
+class JSFixedArray extends JSMutableArray {}
+class JSExtendableArray extends JSMutableArray {}
+class JSString implements JSIndexable {
+  var split;
+  var concat;
+  var toString;
+}
+class JSFunction {}
+class JSInt {}
+class JSDouble {}
+class JSNumber {}
+class JSNull {}
+class JSBool {}
+getInterceptor(o){}
+getDispatchProperty(o) {}
+setDispatchProperty(o, v) {}""";
     } else if (uri.path.endsWith('js_helper.dart')) {
       source = 'library jshelper; class JSInvocationMirror {} '
                'class ConstantMap {} class TypeImpl {}';
     } else if (uri.path.endsWith('isolate_helper.dart')) {
       source = 'library isolatehelper; class _WorkerStub {}';
     } else {
       source = "library lib;";
     }
   } else {
    throw "unexpected URI $uri";
@@ skipping 16 matching lines @@
               new Uri(scheme: 'package', path: '/'),
               provider, handler);
   result.then((String code) {
     if (code == null) {
       throw 'Compilation failed';
     }
   }, onError: (e) {
       throw 'Compilation failed';
   });
 }