Update charted to 0.4.8 and roll

packages/quiver/lib/src/cache/map_cache.dart

 // Copyright 2013 Google Inc. All Rights Reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
 part of quiver.cache;
 
-/**
- * A [Cache] that's backed by a [Map].
- */
+/// A [Cache] that's backed by a [Map].
 class MapCache<K, V> implements Cache<K, V> {
   final Map<K, V> _map;
 
-  /**
-   * Creates a new [MapCache], optionally using [map] as the backing [Map].
-   */
+  /// Creates a new [MapCache], optionally using [map] as the backing [Map].
   MapCache({Map<K, V> map}) : _map = map != null ? map : new HashMap<K, V>();
 
-  /**
-   * Creates a new [MapCache], using [LruMap] as the backing [Map].
-   * Optionally specify [maximumSize].
-   */
+  /// Creates a new [MapCache], using [LruMap] as the backing [Map].
+  /// Optionally specify [maximumSize].
   factory MapCache.lru({int maximumSize}) {
     return new MapCache<K, V>(map: new LruMap(maximumSize: maximumSize));
   }
 
   Future<V> get(K key, {Loader<K> ifAbsent}) {
     if (!_map.containsKey(key) && ifAbsent != null) {
       var valOrFuture = ifAbsent(key);
       if (valOrFuture is Future) {
         return valOrFuture.then((v) {
-          _map[key] = v;
-          return v;
+          _map[key] = v as V;
+          return v as V;
         });
       } else {
-        _map[key] = valOrFuture;
-        return new Future.value(valOrFuture);
+        _map[key] = valOrFuture as V;
+        return new Future<V>.value(valOrFuture);
       }
     }
     return new Future.value(_map[key]);
   }
 
   Future set(K key, V value) {
     _map[key] = value;
     return new Future.value();
   }
 
   Future invalidate(K key) {
     _map.remove(key);
     return new Future.value();
   }
 }