Put back traverseEs6 to ease the transition for external users of the…

… Java API. Fixes #2892

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=193228792

src/com/google/javascript/jscomp/NodeTraversal.java

@@ -712,6 +712,14 @@ public final boolean shouldTraverse(NodeTraversal t, Node n, Node parent) {
         });
   }
 
+  /**
+   * Use #traverse(AbstractCompiler, Node, Callback)
+   */
+  @Deprecated
+  public static final void traverseEs6(AbstractCompiler compiler, Node root, Callback cb) {
+    traverse(compiler, root, cb);
+  }
+
   /** Traverses from a particular scope node using the ES6SyntacticScopeCreator */
   private static void traverseEs6ScopeRoot(
       AbstractCompiler compiler, Node scopeNode, Callback cb, MemoizedScopeCreator scopeCreator) {