Use destructuring assignments for named parameters (#180)

test/codegen/expect/collection/src/canonicalized_map.js

 dart_library.library('collection/src/canonicalized_map', null, /* Imports */[
   "dart/_runtime",
   'dart/core',
   'collection/src/utils',
   'dart/collection'
 ], /* Lazy imports */[
 ], function(exports, dart, core, utils, collection) {
   'use strict';
   let dartx = dart.dartx;
   let _base = Symbol('_base');
   let _canonicalize = Symbol('_canonicalize');
   let _isValidKeyFn = Symbol('_isValidKeyFn');
   let _isValidKey = Symbol('_isValidKey');
   let CanonicalizedMap$ = dart.generic(function(C, K, V) {
     class CanonicalizedMap extends core.Object {
-      CanonicalizedMap(canonicalize, opts) {
-        let isValidKey = opts && 'isValidKey' in opts ? opts.isValidKey : null;
+      CanonicalizedMap(canonicalize, {isValidKey = null} = {}) {
         this[_base] = core.Map$(C, utils.Pair$(K, V)).new();
         this[_canonicalize] = canonicalize;
         this[_isValidKeyFn] = isValidKey;
       }
-      from(other, canonicalize, opts) {
-        let isValidKey = opts && 'isValidKey' in opts ? opts.isValidKey : null;
+      from(other, canonicalize, {isValidKey = null} = {}) {
         this[_base] = core.Map$(C, utils.Pair$(K, V)).new();
         this[_canonicalize] = canonicalize;
         this[_isValidKeyFn] = isValidKey;
         this.addAll(other);
       }
       get(key) {
         if (!dart.notNull(this[_isValidKey](key)))
           return null;
         let pair = this[_base].get(dart.dcall(this[_canonicalize], key));
         return pair == null ? null : pair.last;
@@ skipping 76 matching lines @@
         [_isValidKey]: [core.bool, [core.Object]]
       })
     });
     return CanonicalizedMap;
   });
   let CanonicalizedMap = CanonicalizedMap$();
   // Exports:
   exports.CanonicalizedMap$ = CanonicalizedMap$;
   exports.CanonicalizedMap = CanonicalizedMap;
 });