a === b -> identical(a, b)

runtime/lib/array.dart

Index: runtime/lib/array.dart
diff --git a/runtime/lib/array.dart b/runtime/lib/array.dart
index aa1168f3c998bd9578a0fc619206f7d428825183..b88b66e1158c9bf16068300a8d5f93ef061e894f 100644
--- a/runtime/lib/array.dart
+++ b/runtime/lib/array.dart
@@ -89,7 +89,7 @@ class _ObjectArray<E> implements List<E> {
   }
 
   bool get isEmpty {
-    return this.length === 0;
+    return this.length == 0;
   }
 
   void sort([Comparator<E> compare = Comparable.compare]) {
@@ -101,7 +101,7 @@ class _ObjectArray<E> implements List<E> {
   }
 
   int lastIndexOf(E element, [int start = null]) {
-    if (start === null) start = length - 1;
+    if (start == null) start = length - 1;
     return Arrays.lastIndexOf(this, element, start);
   }
 
@@ -231,7 +231,7 @@ class _ImmutableArray<E> implements List<E> {
   }
 
   bool get isEmpty {
-    return this.length === 0;
+    return this.length == 0;
   }
 
   void sort([Comparator<E> compare]) {
@@ -248,7 +248,7 @@ class _ImmutableArray<E> implements List<E> {
   }
 
   int lastIndexOf(E element, [int start = null]) {
-    if (start === null) start = length - 1;
+    if (start == null) start = length - 1;
     return Arrays.lastIndexOf(this, element, start);
   }