Make mappedBy lazy.

runtime/lib/byte_array.dart

Index: runtime/lib/byte_array.dart
diff --git a/runtime/lib/byte_array.dart b/runtime/lib/byte_array.dart
index d6cd4e430ef3fbfb7a517bc09c3ca14a42d2a102..afe5eb25a36682cfe466e19801d535cc87cbfdca 100644
--- a/runtime/lib/byte_array.dart
+++ b/runtime/lib/byte_array.dart
@@ -132,8 +132,8 @@ abstract class _ByteArrayBase {
     }
   }
 
-  Collection mappedBy(f(element)) {
-    return Collections.mappedBy(this, new List(), f);
+  Iterable mappedBy(f(element)) {
+    return new MappedIterable(this, f);
   }
 
   Dynamic reduce(Dynamic initialValue,
@@ -1612,7 +1612,7 @@ class _ByteArrayView implements ByteArray {
 }
 
 
-class _ByteArrayViewBase {
+class _ByteArrayViewBase extends Collection<int> {
   abstract num operator[](int index);
 
   // Methods implementing the Collection interface.
@@ -1624,27 +1624,6 @@ class _ByteArrayViewBase {
     }
   }
 
-  Collection mappedBy(f(element)) {
-    return Collections.mappedBy(this, new List(), f);
-  }
-
-  Dynamic reduce(Dynamic initialValue,
-                 Dynamic combine(Dynamic initialValue, element)) {
-    return Collections.reduce(this, initialValue, combine);
-  }
-
-  Collection where(bool f(element)) {
-    return Collections.where(this, new List(), f);
-  }
-
-  bool every(bool f(element)) {
-    return Collections.every(this, f);
-  }
-
-  bool some(bool f(element)) {
-    return Collections.some(this, f);;
-  }
-
   bool get isEmpty {
     return this.length == 0;
   }