Adding isNotEmpty property to collection and string.

runtime/lib/array.dart

Index: runtime/lib/array.dart
diff --git a/runtime/lib/array.dart b/runtime/lib/array.dart
index b26f098735b496b6531e2bbcbbe0ef6061bb1f31..cfb640bc01c076d959d31a7d88458025a50cf313 100644
--- a/runtime/lib/array.dart
+++ b/runtime/lib/array.dart
@@ -194,6 +194,8 @@ class _ObjectArray<E> implements List<E> {
     return this.length == 0;
   }
 
+  bool get isNotEmpty => !isEmpty;
+
   Iterable<E> get reversed => IterableMixinWorkaround.reversedList(this);
 
   void sort([int compare(E a, E b)]) {
@@ -445,6 +447,8 @@ class _ImmutableArray<E> implements List<E> {
     return this.length == 0;
   }
 
+  bool get isNotEmpty => !isEmpty;
+
   Iterable<E> get reversed => IterableMixinWorkaround.reversedList(this);
 
   void sort([int compare(E a, E b)]) {