Eliminate the const constructor from the Expando class.

runtime/lib/expando_patch.dart

 // Copyright (c) 2012, 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.
 
 patch class Expando<T> {
   /* patch */ T operator[](Object object) {
     _checkType(object);
-    var weakProperty = _find(this);
-    var list = weakProperty.value;
     var doCompact = false;
     var result = null;
-    for (int i = 0; i < list.length; ++i) {
-      var key = list[i].key;
-      if (key === object) {
-        result = list[i].value;
-        break;
+    if (_data !== null) {

[hausner, 2012/09/13 20:06:48]

If you declare the constructor external and implement it here, it can allocated
the _data field in the constructor and eliminate this test.

[cshapiro, 2012/09/13 21:19:41]

Good idea.  Done.

+      for (int i = 0; i < _data.length; ++i) {
+        var key = _data[i].key;
+        if (key === object) {
+          result = _data[i].value;
+          break;
+        }
+        if (key === null) {
+          doCompact = true;
+          _data[i] = null;
+        }
       }
-      if (key === null) {
-        doCompact = true;
-        list[i] = null;
+      if (doCompact) {
+        _data = _data.filter((e) => (e !== null));
       }
     }
-    if (doCompact) {
-      weakProperty.value = list.filter((e) => (e !== null));
-    }
     return result;
   }
 
   /* patch */ void operator[]=(Object object, T value) {
     _checkType(object);
-    var weakProperty = _find(this);
-    var list = weakProperty.value;
+    if (_data === null) _data = new List();
     var doCompact = false;
     int i = 0;
-    for (; i < list.length; ++i) {
-      var key = list[i].key;
+    for (; i < _data.length; ++i) {
+      var key = _data[i].key;
       if (key === object) {
         break;
       }
       if (key === null) {
         doCompact = true;
-        list[i] = null;
+        _data[i] = null;
       }
     }
-    if (i !== list.length && value === null) {
+    if (i !== _data.length && value === null) {
       doCompact = true;
-      list[i] = null;
-    } else if (i !== list.length) {
-      list[i].value = value;
+      _data[i] = null;
+    } else if (i !== _data.length) {
+      _data[i].value = value;
     } else {
-      list.add(new _WeakProperty(object, value));
+      _data.add(new _WeakProperty(object, value));
     }
     if (doCompact) {
-      weakProperty.value = list.filter((e) => (e !== null));
+      _data = _data.filter((e) => (e !== null));
     }
   }
 
   static _checkType(object) {
     if (object === null) {
       throw new NullPointerException();
     }
     if (object is bool || object is num || object is String) {
       throw new IllegalArgumentException(object);
     }
   }
 
-  static _find(expando) {
-    if (_data === null) _data = new List();
-    var doCompact = false;
-    int i = 0;
-    for (; i < _data.length; ++i) {
-      var key = _data[i].key;
-      if (key == expando) {
-        break;
-      }
-      if (key === null) {
-        doCompact = true;
-        _data[i] = null;
-      }
-    }
-    if (i == _data.length) {
-      _data.add(new _WeakProperty(expando, new List()));
-    }
-    var result = _data[i];
-    if (doCompact) {
-      _data = _data.filter((e) => (e !== null));
-    }
-    return result;
-  }
-
-  static List _data;
+  List _data;
 }