Change NotImplementedException to UnimplementedError.

samples/ui_lib/observable/observable.dart

 // Copyright (c) 2011, 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('observable');
 
 #import('dart:coreimpl');
 
 #source('ChangeEvent.dart');
 #source('EventBatch.dart');
@@ skipping 225 matching lines @@
       }
     }
     return count;
   }
 
   void copyFrom(List<T> src, int srcStart, int dstStart, int count) {
     Arrays.copy(src, srcStart, this, dstStart, count);
   }
 
   void setRange(int start, int length, List from, [int startFrom = 0]) {
-    throw const NotImplementedException();
+    throw new UnimplementedError();
   }
 
   void removeRange(int start, int length) {
-    throw const NotImplementedException();
+    throw new UnimplementedError();
   }
 
   void insertRange(int start, int length, [initialValue = null]) {
-    throw const NotImplementedException();
+    throw new UnimplementedError();
   }
 
   List getRange(int start, int length) {
-    throw const NotImplementedException();
+    throw new UnimplementedError();
   }
 
   // Iterable<T>:
   Iterator<T> iterator() => _internal.iterator();
 
   // Collection<T>:
   Collection<T> filter(bool f(T element)) => _internal.filter(f);
   Collection map(f(T element)) => _internal.map(f);
   bool every(bool f(T element)) => _internal.every(f);
   bool some(bool f(T element)) => _internal.some(f);
@@ skipping 21 matching lines @@
     //              equality check should be done?
     if (newValue !== _value) {
       final oldValue = _value;
       _value = newValue;
       recordPropertyUpdate("value", newValue, oldValue);
     }
   }
 
   T _value;
 }