Add UIImplementationProvider and allow overriding it in AbstractReactActivity

Summary: public UIImplementationProvider allows plugging in an alternative UIImplementation. A follow up diff adds a toggle under FB Dev Settings and uses this class to control an implementation. This allows us experimenting with other ways of generating UI hierarchy from JavaScript components.

Reviewed By: astreet

Differential Revision: D2554774

fb-gh-sync-id: 6574a893020e3519bd2ab00b9620a6dbdfaed595

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

@@ -0,0 +1,24 @@
+/**
+ * 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.uimanager;
+
+import java.util.List;
+
+import com.facebook.react.bridge.ReactApplicationContext;
+
+/**
+ * Provides UIImplementation to use in {@link UIManagerModule}.
+ */
+public class UIImplementationProvider {
+  public UIImplementation createUIImplementation(
+      ReactApplicationContext reactContext,
+      List<ViewManager> viewManagers) {
+    return new UIImplementation(reactContext, viewManagers);
+  }
+}