Use destructuring assignments for named parameters (#180)

test/codegen/expect/collection/wrappers.js

Index: test/codegen/expect/collection/wrappers.js
diff --git a/test/codegen/expect/collection/wrappers.js b/test/codegen/expect/collection/wrappers.js
index 70b2afee44a1593268a0a068933922253d7086d1..49c94d63cb66b7d4ada79fba297d566e8b53f86c 100644
--- a/test/codegen/expect/collection/wrappers.js
+++ b/test/codegen/expect/collection/wrappers.js
@@ -37,9 +37,8 @@ dart_library.library('collection/wrappers', null, /* Imports */[
       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});
       }
@@ -71,9 +70,8 @@ dart_library.library('collection/wrappers', null, /* Imports */[
       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});
       }
@@ -109,8 +107,7 @@ dart_library.library('collection/wrappers', null, /* Imports */[
         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() {