Add AsyncWaiter implementation to java API.

mojo/public/java/src/org/chromium/mojo/system/AsyncWaiter.java

Index: mojo/public/java/src/org/chromium/mojo/system/AsyncWaiter.java
diff --git a/mojo/public/java/src/org/chromium/mojo/system/AsyncWaiter.java b/mojo/public/java/src/org/chromium/mojo/system/AsyncWaiter.java
new file mode 100644
index 0000000000000000000000000000000000000000..f62ac76a11b8623233d29e3a268a9d714aa6fa4a
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+++ b/mojo/public/java/src/org/chromium/mojo/system/AsyncWaiter.java
@@ -0,0 +1,53 @@
+// 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.system;
+
+import org.chromium.mojo.system.Core.WaitFlags;
+
+/**
+ * A class which implements the {@link AsyncWaiter} allows asynchronously waiting on a background
+ * thread.
+ */
+public interface AsyncWaiter {
+
+    /**
+     * Allows cancellation of an asyncWait operation.
+     */
+    interface Cancellable {
+        /**
+         * Cancels an asyncWait operation. Has no effect if the operation has already been canceled
+         * or the callback has already been called.
+         * <p>
+         * Must be called from the same thread as {@link AsyncWaiter#asyncWait} was called from.
+         */
+        void cancel();
+    }
+
+    /**
+     * Callback passed to {@link AsyncWaiter#asyncWait}.
+     */
+    public interface Callback {
+        /**
+         * Called when the handle is ready.
+         */
+        public void onResult(int result);
+
+        /**
+         * Called when an error occurred while waiting.
+         */
+        public void onError(MojoException exception);
+    }
+
+    /**
+     * Asynchronously call wait on a background thread. The given {@link Callback} will be notified
+     * of the result of the wait on the same thread as asyncWait was called.
+     *
+     * @return a {@link Cancellable} object that can be used to cancel waiting. The cancellable
+     *         should only be used on the current thread, and becomes invalid once the callback has
+     *         been notified.
+     */
+    Cancellable asyncWait(Handle handle, WaitFlags flags, long deadline, Callback callback);
+
+}