Lint to prefer x.isNotEmpty vs. !x.isEmpty (#143).

lib/src/sdk.dart

Index: lib/src/sdk.dart
diff --git a/lib/src/sdk.dart b/lib/src/sdk.dart
index 9dfa1de1df5aad698347f4dd8639869d0d98973d..da43a9100cc5084aaf0ea9ca5a7da79cbbf3aab3 100644
--- a/lib/src/sdk.dart
+++ b/lib/src/sdk.dart
@@ -92,6 +92,7 @@ class Iterator<E> {
 abstract class Iterable<E> {
   Iterator<E> get iterator;
   bool get isEmpty;
+  bool get isNotEmpty;
 }
 
 abstract class List<E> implements Iterable<E> {
@@ -100,10 +101,14 @@ abstract class List<E> implements Iterable<E> {
   void operator []=(int index, E value);
   Iterator<E> get iterator => null;
   void clear();
+  bool get isEmpty;
+  bool get isNotEmpty;
 }
 
 abstract class Map<K, V> extends Object {
   Iterable<K> get keys;
+  bool get isEmpty;
+  bool get isNotEmpty;
 }
 
 external bool identical(Object a, Object b);