/*
 * Copyright 2016 The Closure Compiler Authors.
 *
 * 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.
 */
package com.google.javascript.jscomp;

import com.google.common.collect.ImmutableList;
import com.google.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
import com.google.javascript.rhino.Node;

/**
 * Finds the externs for the PolymerElement base class and all of its properties in the externs.
 */
final class PolymerPassFindExterns extends AbstractPostOrderCallback {

  private static final String POLYMER_ELEMENT_NAME = "PolymerElement";

  private Node polymerElementExterns;
  private final ImmutableList.Builder<Node> polymerElementProps;

  PolymerPassFindExterns() {
    polymerElementProps = ImmutableList.builder();
  }

  @Override
  public void visit(NodeTraversal t, Node n, Node parent) {
    if (isPolymerElementExterns(n)) {
      polymerElementExterns = n;
    } else if (isPolymerElementPropExpr(n)) {
      polymerElementProps.add(n);
    }
  }

  /**
   * @return All properties of the {@code PolymerElement} class in externs.
   */
  ImmutableList<Node> getPolymerElementProps() {
    return polymerElementProps.build();
  }

  /**
   * @return The root {@link Node} {@code PolymerElement} class in externs.
   */
  Node getPolymerElementExterns() {
    return polymerElementExterns;
  }

  /**
   * @return Whether the node is the declaration of PolymerElement.
   */
  private static boolean isPolymerElementExterns(Node value) {
    return value != null && value.isVar()
        && value.getFirstChild().matchesQualifiedName(POLYMER_ELEMENT_NAME);
  }

  /**
   * @return Whether the node is an expression result of an assignment to a property of
   * PolymerElement.
   */
  private static boolean isPolymerElementPropExpr(Node value) {
    return value != null
        && value.isExprResult()
        && value.getFirstFirstChild() != null
        && value.getFirstFirstChild().isGetProp()
        && value.getFirstFirstChild().isQualifiedName()
        && NodeUtil.getRootOfQualifiedName(
            value.getFirstFirstChild()).matchesQualifiedName(POLYMER_ELEMENT_NAME);
  }
}

@@ -1980,44 +1980,90 @@
     
-return value != null && value.isVar(
+// Explicitly allow var, let or const.%0A    return NodeUtil.isNameDeclaration(value
 )%0A  

Update the Polymer pass to allow for let, var or const as the declaration type for matching PolymerExterns. (They should be consistent, but at least this allows us freedom in future).