Android plumbing for State and LocalData update mount items

Summary: Android plumbing for State and LocalData update mount items. See other commits in stack for usage

Reviewed By: mdvacca

Differential Revision: D14663522

fbshipit-source-id: 5604a6a9af292805e9ce46c68e5ce7472eef0218

ReactAndroid/src/main/java/com/facebook/react/uimanager/StateWrapper.java

@@ -0,0 +1,29 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc.
+ *
+ * <p>This source code is licensed under the MIT license found in the LICENSE file in the root
+ * directory of this source tree.
+ */
+package com.facebook.react.uimanager;
+
+import com.facebook.react.bridge.ReadableNativeMap;
+import com.facebook.react.bridge.WritableMap;
+
+/**
+ * This is a wrapper that can be used for passing State objects from Fabric C++
+ * core to platform-specific components in Java.
+ * State allows you to break out of uni-directional dataflow by calling updateState,
+ * which communicates state back to the C++ layer.
+ */
+public interface StateWrapper {
+  /**
+   * Get a ReadableNativeMap object from the C++ layer, which is a K/V map of
+   * string keys to values.
+   */
+  ReadableNativeMap getState();
+
+  /**
+   * Pass a map of values back to the C++ layer.
+   */
+  void updateState(WritableMap map);
+}