Support for WindowContainer controllers and listeners

- WindowContainerController class allows a component outside window manager
to create a window container and communicate directly with it to make
changes. For example, the ActivityRecord class in activity manager uses the
AppWindowContainerController class to create and communicate with
AppWindowToken window container class which is its counterpart on the window
manager side.
- WindowContainerListener interface allows a component outside WM to get
notified of changes to a window container. For example, the ActivityRecord
class in AM implements the AppWindowContainerListener interface to get
notified of changes to the AppWindowToken container.

Bug: 30060889
Test: Existing tests pass and manual testing.
Test: bit FrameworksServicesTests:com.android.server.wm.WindowContainerControllerTests
Test: bit FrameworksServicesTests:com.android.server.wm.WindowContainerTests
Change-Id: I2896bfa46a80b227052528c7da8cf4e56beab4bc
diff --git a/services/core/java/com/android/server/wm/WindowContainerListener.java b/services/core/java/com/android/server/wm/WindowContainerListener.java
new file mode 100644
index 0000000..ab9d71a
--- /dev/null
+++ b/services/core/java/com/android/server/wm/WindowContainerListener.java
@@ -0,0 +1,25 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * 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.android.server.wm;
+
+/**
+ * Interface used by the owner/creator of the container to listen to changes with the container.
+ * @see WindowContainerController
+ */
+public interface WindowContainerListener {
+
+}