Strong mode fixes for package

BUG=
R=kevmoo@google.com

Review URL: https://codereview.chromium.org//2560823004 .
diff --git a/lib/dom.dart b/lib/dom.dart
index 63182f6..bd3e2bd 100644
--- a/lib/dom.dart
+++ b/lib/dom.dart
@@ -809,7 +809,6 @@
 // TODO(jmesserly): "implements List<Element>" is a workaround for analyzer bug.
 class FilteredElementList extends IterableBase<Element> with ListMixin<Element>
     implements List<Element> {
-  final Node _node;
   final List<Node> _childNodes;
 
   /// Creates a collection of the elements that descend from a node.
@@ -819,8 +818,8 @@
   ///     var filteredElements = new FilteredElementList(query("#container"));
   ///     // filteredElements is [a, b, c].
   FilteredElementList(Node node)
-      : _childNodes = node.nodes,
-        _node = node;
+      : _childNodes = node.nodes;
+
 
   // We can't memoize this, since it's possible that children will be messed
   // with externally to this class.
diff --git a/lib/src/encoding_parser.dart b/lib/src/encoding_parser.dart
index 0b84989..9da260b 100644
--- a/lib/src/encoding_parser.dart
+++ b/lib/src/encoding_parser.dart
@@ -200,7 +200,6 @@
         }
       }
     }
-    return true; // unreachable
   }
 
   bool handlePossibleStartTag() => handlePossibleTag(false);
@@ -322,7 +321,6 @@
         attrValue.add(c);
       }
     }
-    return null; // unreachable
   }
 }