[Android] Allow text handles to observe position of "parent" view

content/public/android/java/src/org/chromium/content/browser/PositionObserver.java

+// Copyright 2013 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.content.browser;
+
+/**
+ * Used to register listeners that can be notified of changes to the position of a view.
+ */
+public interface PositionObserver {
+    public interface Listener {
+        /**
+         * Called during predraw if the position of the underlying view has changed.
+         */
+        void onPositionChanged(int positionX, int positionY);
+    }
+
+    /**
+     * @return The current x position of the observed view.
+     */
+    int getPositionX();
+
+    /**
+     * @return The current y position of the observed view.
+     */
+    int getPositionY();
+
+    /**
+     * Register a listener to be called when the position of the underlying view changes.
+     */
+    void addListener(Listener listener);
+
+    /**
+     * Remove a previously installed listener.
+     */
+    void removeListener(Listener listener);
+}