fix #603, support mock objects

test/codegen_expected/language/no_such_method_mock_test.js

+dart_library.library('language/no_such_method_mock_test', null, /* Imports */[
+  'dart_sdk',
+  'expect'
+], function load__no_such_method_mock_test(exports, dart_sdk, expect) {
+  'use strict';
+  const core = dart_sdk.core;
+  const dart = dart_sdk.dart;
+  const dartx = dart_sdk.dartx;
+  const expect$ = expect.expect;
+  const no_such_method_mock_test = Object.create(null);
+  let VoidToint = () => (VoidToint = dart.constFn(dart.definiteFunctionType(core.int, [])))();
+  let VoidTovoid = () => (VoidTovoid = dart.constFn(dart.definiteFunctionType(dart.void, [])))();
+  no_such_method_mock_test.Cat = class Cat extends core.Object {
+    eatFood(food) {
+      return true;
+    }
+    scratch(furniture) {
+      return 100;
+    }
+  };
+  dart.setSignature(no_such_method_mock_test.Cat, {
+    methods: () => ({
+      eatFood: dart.definiteFunctionType(core.bool, [core.String]),
+      scratch: dart.definiteFunctionType(core.int, [core.String])
+    })
+  });
+  no_such_method_mock_test.MockCat = class MockCat extends core.Object {
+    noSuchMethod(invocation) {
+      return core.String.as(invocation.positionalArguments[dartx.get](0))[dartx.isNotEmpty];
+    }
+    eatFood(food) {
+      return core.bool._check(this.noSuchMethod(new dart.InvocationImpl('eatFood', [food], {isMethod: true})));
+    }
+    scratch(furniture) {
+      return core.int._check(this.noSuchMethod(new dart.InvocationImpl('scratch', [furniture], {isMethod: true})));
+    }
+  };
+  no_such_method_mock_test.MockCat[dart.implements] = () => [no_such_method_mock_test.Cat];
+  no_such_method_mock_test.main = function() {
+    let mock = new no_such_method_mock_test.MockCat();
+    expect$.Expect.isTrue(dart.dsend(mock, 'eatFood', "food"));
+    expect$.Expect.isFalse(mock.eatFood(""));
+    expect$.Expect.throws(dart.fn(() => dart.notNull(mock.scratch("couch")) + 0, VoidToint()));
+  };
+  dart.fn(no_such_method_mock_test.main, VoidTovoid());
+  // Exports:
+  exports.no_such_method_mock_test = no_such_method_mock_test;
+});