simplify constructors, fixes #564

test/codegen/expect/fieldtest.js

 dart_library.library('fieldtest', null, /* Imports */[
   'dart_sdk'
 ], function(exports, dart_sdk) {
   'use strict';
   const core = dart_sdk.core;
   const dart = dart_sdk.dart;
   const dartx = dart_sdk.dartx;
   const fieldtest = Object.create(null);
   fieldtest.A = class A extends core.Object {
-    A() {
+    new() {
       this.x = 42;
     }
   };
   fieldtest.B$ = dart.generic(T => {
     class B extends core.Object {
-      B() {
+      new() {
         this.x = null;
         this.y = null;
         this.z = null;
       }
     }
     return B;
   });
   fieldtest.B = fieldtest.B$();
   fieldtest.foo = function(a) {
     core.print(a.x);
@@ skipping 31 matching lines @@
     set z(value) {
       fieldtest.y = dart.as(value, core.int);
     }
   });
   fieldtest.BaseWithGetter = class BaseWithGetter extends core.Object {
     get foo() {
       return 1;
     }
   };
   fieldtest.Derived = class Derived extends fieldtest.BaseWithGetter {
-    Derived() {
+    new() {
       this[foo] = 2;
       this.bar = 3;
     }
     get foo() {
       return this[foo];
     }
     set foo(value) {
       this[foo] = value;
     }
   };
@@ skipping 32 matching lines @@
       return fieldtest.StaticFieldOrder2.b + 1;
     },
     get c() {
       return fieldtest.StaticFieldOrder2.d + 2;
     },
     get b() {
       return fieldtest.StaticFieldOrder2.c + 3;
     }
   });
   fieldtest.MyEnum = class MyEnum extends core.Object {
-    MyEnum(index) {
+    new(index) {
       this.index = index;
     }
     toString() {
       return {
         0: "MyEnum.Val1",
         1: "MyEnum.Val2",
         2: "MyEnum.Val3",
         3: "MyEnum.Val4"
       }[this.index];
     }
   };
   fieldtest.MyEnum.Val1 = dart.const(new fieldtest.MyEnum(0));
   fieldtest.MyEnum.Val2 = dart.const(new fieldtest.MyEnum(1));
   fieldtest.MyEnum.Val3 = dart.const(new fieldtest.MyEnum(2));
   fieldtest.MyEnum.Val4 = dart.const(new fieldtest.MyEnum(3));
   fieldtest.MyEnum.values = dart.const(dart.list([fieldtest.MyEnum.Val1, fieldtest.MyEnum.Val2, fieldtest.MyEnum.Val3, fieldtest.MyEnum.Val4], fieldtest.MyEnum));
   fieldtest.main = function() {
     let a = new fieldtest.A();
     fieldtest.foo(a);
     fieldtest.bar(a);
     core.print(fieldtest.baz(a));
     core.print(new (fieldtest.Generic$(core.String))().foo(' world'));
     core.print(fieldtest.MyEnum.values);
   };
   dart.fn(fieldtest.main, dart.void, []);
   // Exports:
   exports.fieldtest = fieldtest;
 });