Adding isNotEmpty property to collection and string.

sdk/lib/collection/iterable.dart

Index: sdk/lib/collection/iterable.dart
diff --git a/sdk/lib/collection/iterable.dart b/sdk/lib/collection/iterable.dart
index 2ec143b8c495e2a462275c06b3f4118b4b9cb5fa..a9505432dd30f91ebfb62596764fd25fbc2ec4be 100644
--- a/sdk/lib/collection/iterable.dart
+++ b/sdk/lib/collection/iterable.dart
@@ -95,6 +95,8 @@ abstract class IterableMixin<E> implements Iterable<E> {
 
   bool get isEmpty => !iterator.moveNext();
 
+  bool get isNotEmpty => !isEmpty;
+
   Iterable<E> take(int n) {
     return new TakeIterable<E>(this, n);
   }
@@ -287,6 +289,8 @@ abstract class IterableBase<E> implements Iterable<E> {
 
   bool get isEmpty => !iterator.moveNext();
 
+  bool get isNotEmpty => !isEmpty;
+
   Iterable<E> take(int n) {
     return new TakeIterable<E>(this, n);
   }