Update charted to 0.4.8 and roll

packages/quiver/lib/testing/src/runtime/checked_mode.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.testing.runtime;
 
-/**
- * Asserts that the current runtime has checked mode enabled.
- *
- * Otherwise, throws [StateError].
- */
+/// Asserts that the current runtime has checked mode enabled.
+///
+/// Otherwise, throws [StateError].
 void assertCheckedMode() {
   if (_isCheckedMode == null) _isCheckedMode = _checkForCheckedMode();
 
   if (!_isCheckedMode) {
     throw new StateError('Not in checked mode.');
   }
 }
 
 bool _isCheckedMode = null;
 
 bool _checkForCheckedMode() {
   Object sentinal = new Object();
   try {
     var i = 1 as dynamic;
-    String string = i;
+    _takeString(i);
     throw sentinal;
   } catch (e) {
     if (e == sentinal) return false;
   }
   return true;
 }
+
+void _takeString(String value) {}