Detach dependency on RRV for Instance Manager

Summary: Remove dependency on ReactRootView in ReactInstanceManager by creating a rough interface (ReactRoot) so that either a Surface or ReactRootView can be attached to ReactInstanceManager.

Reviewed By: ejanzer, mdvacca

Differential Revision: D14158890

fbshipit-source-id: b7ab4654b1e0ef8343230a3c15023653a7f23a4b

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

@@ -0,0 +1,50 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * 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 android.os.Bundle;
+import android.view.ViewGroup;
+import com.facebook.react.uimanager.common.UIManagerType;
+import javax.annotation.Nullable;
+
+
+/**
+ * Interface for the root native view of a React native application
+ */
+public interface ReactRoot {
+
+  /**
+   * Return cached launch properties for app
+   */
+  @Nullable Bundle getAppProperties();
+  @Nullable String getInitialUITemplate();
+
+  /**
+   * Fabric or Default UI Manager, see {@link UIManagerType}
+   */
+  @UIManagerType int getUIManagerType();
+
+  int getRootViewTag();
+
+  void setRootViewTag(int rootViewTag);
+
+  /**
+   * Calls into JS to start the React application.
+   */
+  void runApplication();
+
+  /**
+   * Handler for stages {@link com.facebook.react.surface.ReactStage}
+   */
+  void onStage(int stage);
+
+  /**
+   * Return native view for root
+   */
+  ViewGroup getRootViewGroup();
+}