Cleanup of various DOM dart2js and dart_analyzer warnings

tools/dom/templates/html/impl/impl_Node.darttemplate

 // 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 $LIBRARYNAME;
 
 /**
  * Lazy implementation of the child nodes of an element that does not request
  * the actual child nodes of an element until strictly necessary greatly
  * improving performance for the typical cases where it is not required.
@@ skipping 39 matching lines @@
     return _this.$dom_firstChild;
   }
 $endif
 
   void add(Node value) {
     _this.append(value);
   }
 
   void addAll(Iterable<Node> iterable) {
     if (iterable is _ChildNodeListLazy) {
-      if (!identical(iterable._this, _this)) {
+      _ChildNodeListLazy otherList = iterable;
+      if (!identical(otherList._this, _this)) {
         // Optimized route for copying between nodes.
-        for (var i = 0, len = iterable.length; i < len; ++i) {
+        for (var i = 0, len = otherList.length; i < len; ++i) {
           // Should use $dom_firstChild, Bug 8886.
-          _this.append(iterable[0]);
+          _this.append(otherList[0]);
         }
       }
       return;
     }
     for (Node node in iterable) {
       _this.append(node);
     }
   }
 
   void insert(int index, Node node) {
@@ skipping 198 matching lines @@
   TemplateInstance _templateInstance;
 
   /** Gets the template instance that instantiated this node, if any. */
   @Experimental
   TemplateInstance get templateInstance =>
       _templateInstance != null ? _templateInstance :
       (parent != null ? parent.templateInstance : null);
 
 $!MEMBERS
 }