dart2js: Fix hints in code base.

pkg/compiler/lib/src/dart_backend/placeholder_collector.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_backend;
 
 class LocalPlaceholder {
   final String identifier;
   final Set<Node> nodes;
   LocalPlaceholder(this.identifier) : nodes = new Set<Node>();
@@ skipping 319 matching lines @@
     declarationTypePlaceholders.add(
         new DeclarationTypePlaceholder(type, false));
   }
 
   void makeVarDeclarationTypePlaceholder(VariableDefinitions node) {
     // TODO(smok): Maybe instead of calling this method and
     // makeDeclaratioTypePlaceholder have type declaration placeholder
     // collector logic in visitVariableDefinitions when resolver becomes better
     // and/or catch syntax changes.
     if (node.type == null) return;
-    Element definitionElement = treeElements[node.definitions.nodes.head];
     bool requiresVar = !node.modifiers.isFinalOrConst;
     declarationTypePlaceholders.add(
         new DeclarationTypePlaceholder(node.type, requiresVar));
   }
 
   /// Marks [node] to be erased in the output.
   /// This is done for library prefixes because they are not used in the output
   /// because all imports are flattened and conflicts are renamed away.
   void makeErasePrefixPlaceholder(Node node) {
     assert(node is Identifier || node is Send);
@@ skipping 367 matching lines @@
 
   visitBlock(Block node) {
     for (Node statement in node.statements.nodes) {
       if (statement is VariableDefinitions) {
         makeVarDeclarationTypePlaceholder(statement);
       }
     }
     node.visitChildren(this);
   }
 }