Change NotImplementedException to UnimplementedError.

samples/ui_lib/observable/observable.dart

Index: samples/ui_lib/observable/observable.dart
diff --git a/samples/ui_lib/observable/observable.dart b/samples/ui_lib/observable/observable.dart
index 7cf33a09474677cf8a16a9a3decd480a8dcaf0d3..48b42f4fc4737610b187885ea3a83bdba11de928 100644
--- a/samples/ui_lib/observable/observable.dart
+++ b/samples/ui_lib/observable/observable.dart
@@ -243,19 +243,19 @@ class ObservableList<T>
   }
 
   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>: