Tighten a couple type annotations in IterableMixin

sdk/lib/collection/iterable.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart.collection;
 
 /**
  * This [Iterable] mixin implements all [Iterable] members except `iterator`.
  *
  * All other methods are implemented in terms of `iterator`.
@@ skipping 129 matching lines @@
   }
 
   E get single {
     Iterator it = iterator;
     if (!it.moveNext()) throw IterableElementError.noElement();
     E result = it.current;
     if (it.moveNext()) throw IterableElementError.tooMany();
     return result;
   }
 
-  dynamic firstWhere(bool test(E value), { Object orElse() }) {
+  E firstWhere(bool test(E value), { E orElse() }) {
     for (E element in this) {
       if (test(element)) return element;
     }
     if (orElse != null) return orElse();
     throw IterableElementError.noElement();
   }
 
-  dynamic lastWhere(bool test(E value), { Object orElse() }) {
+  E lastWhere(bool test(E value), { E orElse() }) {
     E result = null;
     bool foundMatching = false;
     for (E element in this) {
       if (test(element)) {
         result = element;
         foundMatching = true;
       }
     }
     if (foundMatching) return result;
     if (orElse != null) return orElse();
@@ skipping 167 matching lines @@
   }
 
   E get single {
     Iterator it = iterator;
     if (!it.moveNext()) throw IterableElementError.noElement();
     E result = it.current;
     if (it.moveNext()) throw IterableElementError.tooMany();
     return result;
   }
 
-  dynamic firstWhere(bool test(E value), { Object orElse() }) {
+  E firstWhere(bool test(E value), { E orElse() }) {
     for (E element in this) {
       if (test(element)) return element;
     }
     if (orElse != null) return orElse();
     throw IterableElementError.noElement();
   }
 
-  dynamic lastWhere(bool test(E value), { Object orElse() }) {
+  E lastWhere(bool test(E value), { E orElse() }) {
     E result = null;
     bool foundMatching = false;
     for (E element in this) {
       if (test(element)) {
         result = element;
         foundMatching = true;
       }
     }
     if (foundMatching) return result;
     if (orElse != null) return orElse();
@@ skipping 226 matching lines @@
         length += ELLIPSIS_SIZE + OVERHEAD;
       }
     }
     if (elision != null) {
       parts.add(elision);
     }
     parts.add(penultimateString);
     parts.add(ultimateString);
   }
 }