Fix typo in EfficientLengthIterable documentation, and improve it slightly.

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 393 matching lines @@
  * [length] getter.
  *
  * An iterable implementing this interface should have an "efficient"
  * implementation of `length` that doesn't trigger iteration of the
  * iterable. Being efficient doesn't necessarily require being constant
  * time, but should at least attempt to have have execution time that is
  * better than linear in the elements of the iterable.
  *
  * Methods that worry about reading the length of an `Iterable` because it
  * may be inefficient or may trigger side-effects, or may even never complete,
- * can first check if the iterable `is EfficientLengthIterableIterable`,
+ * can first check if the iterable `is EfficientLengthIterable`,
  * and if so, use [length] without those concerns.
  *
- * The `EfficientLengthIterable` type should never be used as an API type
+ * The `EfficientLengthIterable` type should never be used as a type
  * assertion - neither as argument type or return type of a function.
  * Always use [Iterable] for the type and just document the performance if it
  * is relevant. This avoids needlessly restricting the values that can be used.
  */
 abstract class EfficientLengthIterable<T> implements Iterable<T> {
   /**
    * Returns the number of elements in the iterable.
    *
    * This is an efficient operation that doesn't iterate through
    * the elements.
    */
   int get length;
 }