Use destructuring assignments for named parameters (#180)

lib/runtime/dart/_internal.js

Index: lib/runtime/dart/_internal.js
diff --git a/lib/runtime/dart/_internal.js b/lib/runtime/dart/_internal.js
index b79ef83a4f98bdb1e07b2761578847c90b801383..4823c44738fd77b7a407b20a2fda82c14df2e489 100644
--- a/lib/runtime/dart/_internal.js
+++ b/lib/runtime/dart/_internal.js
@@ -83,9 +83,8 @@ dart_library.library('dart/_internal', null, /* Imports */[
         }
         return false;
       }
-      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, []));
         let length = this.length;
         for (let i = 0; dart.notNull(i) < dart.notNull(length); i = dart.notNull(i) + 1) {
@@ -100,9 +99,8 @@ dart_library.library('dart/_internal', null, /* Imports */[
           return orElse();
         dart.throw(IterableElementError.noElement());
       }
-      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, []));
         let length = this.length;
         for (let i = dart.notNull(length) - 1; dart.notNull(i) >= 0; i = dart.notNull(i) - 1) {
@@ -218,8 +216,7 @@ dart_library.library('dart/_internal', null, /* Imports */[
         dart.as(test, dart.functionType(core.bool, [E]));
         return super.takeWhile(test);
       }
-      toList(opts) {
-        let growable = opts && 'growable' in opts ? opts.growable : true;
+      toList({growable = true} = {}) {
         let result = null;
         if (dart.notNull(growable)) {
           result = core.List$(E).new();
@@ -357,8 +354,7 @@ dart_library.library('dart/_internal', null, /* Imports */[
           return new (SubListIterable$(E))(this[_iterable], this[_start], newEnd);
         }
       }
-      toList(opts) {
-        let growable = opts && 'growable' in opts ? opts.growable : true;
+      toList({growable = true} = {}) {
         let start = this[_start];
         let end = this[_iterable][dartx.length];
         if (this[_endOrLength] != null && dart.notNull(this[_endOrLength]) < dart.notNull(end))
@@ -972,25 +968,22 @@ dart_library.library('dart/_internal', null, /* Imports */[
         dart.as(test, dart.functionType(core.bool, [E]));
         return false;
       }
-      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, []));
         if (orElse != null)
           return orElse();
         dart.throw(IterableElementError.noElement());
       }
-      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, []));
         if (orElse != null)
           return orElse();
         dart.throw(IterableElementError.noElement());
       }
-      singleWhere(test, opts) {
+      singleWhere(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, []));
         if (orElse != null)
           return orElse();
@@ -1033,8 +1026,7 @@ dart_library.library('dart/_internal', null, /* Imports */[
         dart.as(test, dart.functionType(core.bool, [E]));
         return this;
       }
-      toList(opts) {
-        let growable = opts && 'growable' in opts ? opts.growable : true;
+      toList({growable = true} = {}) {
         return dart.notNull(growable) ? dart.list([], E) : core.List$(E).new(0);
       }
       toSet() {