Allow FlatShadowNode mouting to its own view

Summary: @public This diff adds a `FlatShadowNode.forceMountToView()` method that will render its contents in it own `View`.

Reviewed By: sriramramani

Differential Revision: D2564502

ReactAndroid/src/main/java/com/facebook/react/flat/FlatViewManager.java

@@ -0,0 +1,25 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+package com.facebook.react.flat;
+
+import com.facebook.react.uimanager.ThemedReactContext;
+import com.facebook.react.uimanager.ViewManager;
+
+abstract class FlatViewManager<C extends FlatShadowNode> extends ViewManager<FlatViewGroup, C> {
+
+  @Override
+  protected FlatViewGroup createViewInstance(ThemedReactContext reactContext) {
+    return new FlatViewGroup(reactContext);
+  }
+
+  @Override
+  public void updateExtraData(FlatViewGroup root, Object extraData) {
+  }
+}