Adding a router class to handle messages that expect responses.

mojo/bindings/java/src/org/chromium/mojo/bindings/BindingsHelper.java

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.mojo.bindings;
 
+import org.chromium.mojo.system.AsyncWaiter;
+import org.chromium.mojo.system.Handle;
+
 /**
  * Helper functions.
  */
 public class BindingsHelper {
     /**
      * Alignment in bytes for mojo serialization.
      */
     public static final int ALIGNMENT = 8;
 
     /**
@@ skipping 49 matching lines @@
     }
 
     /**
      * Determines if the given {@code char} value is a Unicode <i>surrogate code unit</i>. See
      * {@link Character#isSurrogate}. Extracting here because the method only exists at API level
      * 19.
      */
     private static boolean isSurrogate(char c) {
         return c >= Character.MIN_SURROGATE && c < (Character.MAX_SURROGATE + 1);
     }
+
+    /**
+     * Returns an {@link AsyncWaiter} to use with the given handle, or <code>null</code> if none if
+     * available.
+     */
+    static AsyncWaiter getDefaultAsyncWaiterForHandle(Handle handle) {
+        if (handle.getCore() != null) {
+            return handle.getCore().getDefaultAsyncWaiter();
+        } else {
+            return null;
+        }
+    }
+
 }