Use destructuring assignments for named parameters (#180)

test/codegen/expect/collection/wrappers.js

 dart_library.library('collection/wrappers', null, /* Imports */[
   "dart/_runtime",
   'collection/src/canonicalized_map',
   'dart/core',
   'dart/math',
   'dart/collection'
 ], /* Lazy imports */[
   'collection/src/unmodifiable_wrappers'
 ], function(exports, dart, canonicalized_map, core, math, collection, unmodifiable_wrappers) {
   'use strict';
@@ skipping 19 matching lines @@
         dart.as(test, dart.functionType(core.bool, [E]));
         return this[_base][dartx.every](test);
       }
       expand(f) {
         dart.as(f, dart.functionType(core.Iterable, [E]));
         return this[_base][dartx.expand](f);
       }
       get first() {
         return this[_base][dartx.first];
       }
-      firstWhere(test, opts) {
+      firstWhere(test, {orElse = null} = {}) {
         dart.as(test, dart.functionType(core.bool, [E]));
-        let orElse = opts && 'orElse' in opts ? opts.orElse : null;
         dart.as(orElse, dart.functionType(E, []));
         return this[_base][dartx.firstWhere](test, {orElse: orElse});
       }
       fold(initialValue, combine) {
         dart.as(combine, dart.functionType(dart.dynamic, [dart.dynamic, E]));
         return this[_base][dartx.fold](initialValue, combine);
       }
       forEach(f) {
         dart.as(f, dart.functionType(dart.void, [E]));
         return this[_base][dartx.forEach](f);
@@ skipping 11 matching lines @@
         return new dart.JsIterator(this.iterator);
       }
       join(separator) {
         if (separator === void 0)
           separator = "";
         return this[_base][dartx.join](separator);
       }
       get last() {
         return this[_base][dartx.last];
       }
-      lastWhere(test, opts) {
+      lastWhere(test, {orElse = null} = {}) {
         dart.as(test, dart.functionType(core.bool, [E]));
-        let orElse = opts && 'orElse' in opts ? opts.orElse : null;
         dart.as(orElse, dart.functionType(E, []));
         return this[_base][dartx.lastWhere](test, {orElse: orElse});
       }
       get length() {
         return this[_base][dartx.length];
       }
       map(f) {
         dart.as(f, dart.functionType(dart.dynamic, [E]));
         return this[_base][dartx.map](f);
       }
@@ skipping 15 matching lines @@
         dart.as(test, dart.functionType(core.bool, [E]));
         return this[_base][dartx.skipWhile](test);
       }
       take(n) {
         return this[_base][dartx.take](n);
       }
       takeWhile(test) {
         dart.as(test, dart.functionType(core.bool, [E]));
         return this[_base][dartx.takeWhile](test);
       }
-      toList(opts) {
-        let growable = opts && 'growable' in opts ? opts.growable : true;
+      toList({growable = true} = {}) {
         return this[_base][dartx.toList]({growable: growable});
       }
       toSet() {
         return this[_base][dartx.toSet]();
       }
       where(test) {
         dart.as(test, dart.functionType(core.bool, [E]));
         return this[_base][dartx.where](test);
       }
       toString() {
@@ skipping 692 matching lines @@
   exports.DelegatingSet$ = DelegatingSet$;
   exports.DelegatingSet = DelegatingSet;
   exports.DelegatingQueue$ = DelegatingQueue$;
   exports.DelegatingQueue = DelegatingQueue;
   exports.DelegatingMap$ = DelegatingMap$;
   exports.DelegatingMap = DelegatingMap;
   exports.MapKeySet$ = MapKeySet$;
   exports.MapValueSet$ = MapValueSet$;
   exports.MapValueSet = MapValueSet;
 });