Update to use one less proxy per element

lib/init.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 library polymer.lib.init;
 
 import 'dart:async';
 import 'dart:js';
+import 'package:reflectable/reflectable.dart';
 import 'package:web_components/web_components.dart';
 import 'src/common/js_proxy.dart';
 import 'src/common/polymer_register.dart';
 
 main() => initPolymer();
 
 Future initPolymer() async {
   await initWebComponents(typeFilter: [HtmlImport], initAll: false);
-  // Make sure `src/js/polymer_array_methods.html` is loaded first.
-  _setUpListMethods();
+  // Make sure polymer is loaded first.
+  _setUpPropertyChanged();
   await initWebComponents(
       typeFilter: [CustomElement, CustomElementProxy, PolymerRegister],
       initAll: true);
 }
 
-void _setUpListMethods() {
-  var polymerDart = context['Polymer']['Dart'];
-  polymerDart['push'] = (List list, Iterable items) {
-    list.addAll(items.map((item) => dartValue(item)));
-  };
-  polymerDart['pop'] = (List list) => list.removeLast();
-  polymerDart['shift'] = (List list) => list.removeAt(0);
-  polymerDart['unshift'] = (List list, Iterable items) {
-    list.insertAll(0, items.map((item) => dartValue(item)));
-  };
-  polymerDart['splice'] =
-      (List list, int start, int deleteCount, Iterable items) {
-    if (start < 0) start = list.length + start;
-    if (deleteCount > 0) list.removeRange(start, start + deleteCount);
-    list.insertAll(start, items.map((item) => dartValue(item)));
+final _polymerDart = context['Polymer']['Dart'];
+
+void _setUpPropertyChanged() {
+  _polymerDart['propertyChanged'] = (instance, String path, newValue) {
+    if (instance is List) {
+      // We only care about `splices` for Lists. This does mean we don't support
+      // setting special properties of custom List implementations though.
+      if (path == 'splices') {
+        // Only apply splices once, if multiple elements have a binding set up
+        // for the same list then they will each get called here.
+        var alreadyApplied = newValue['_applied'];
+        if (alreadyApplied == true) return;
+        newValue['_applied'] = true;
+
+        var splices = newValue['indexSplices'];
+        for (var splice in splices) {
+          var index = splice['index'];
+          var removed = splice['removed'];
+          if (removed != null && removed.length > 0) {
+            instance.removeRange(index, index + removed.length);
+          }
+          var addedCount = splice['addedCount'];
+          var original = splice['object'] as JsArray;
+          instance.insertAll(index,
+              original.getRange(index, addedCount + index).map(dartValue));
+        }
+      } else if (path == 'length') {
+        // Ignore this case, wait for `splices`.
+        return;
+      } else {
+        try {
+          var index = int.parse(path);
+          instance[index] = dartValue(newValue);
+        } on FormatException catch (_) {
+          throw 'Only `splices`, `length`, and index paths are supported for '
+              'list types, found $path.';
+        }
+      }
+    } else if (instance is Map) {
+      instance[path] = dartValue(newValue);
+    } else {
+      var instanceMirror = jsProxyReflectable.reflect(instance);
+      // Catch errors for read only properties. Checking for setters using
+      // reflection is too slow.
+      // https://github.com/dart-lang/polymer-dart/issues/590
+      try {
+        instanceMirror.invokeSetter(path, dartValue(newValue));
+      } on NoSuchMethodError catch (_) {} on NoSuchCapabilityError catch (_) {
+        // TODO(jakemac): Remove once
+        // https://github.com/dart-lang/reflectable/issues/30 is fixed.
+      }
+    }
   };
 }