Mutate shared ReactShadowNode during Fabric.appendChild

Reviewed By: shergin

Differential Revision: D7495539

fbshipit-source-id: 2b2b06d3d4f02a00b01c7ed27d47b61787ea922f

ReactAndroid/src/main/java/com/facebook/react/fabric/FabricUIManager.java

@@ -216,6 +216,12 @@ public void appendChild(ReactShadowNode parent, ReactShadowNode child) {
       Log.d(TAG, "appendChild \n\tparent: " + parent + "\n\tchild: " + child);
     }
     try {
+      // If the child to append is shared with another tree (child.getParent() != null),
+      // then we add a mutation of it. In the future this will be performed by FabricJS / Fiber.
+      //TODO: T27926878 avoid cloning shared child
+      if (child.getParent() != null) {
+        child = child.mutableCopy();
+      }
       parent.addChildAt(child, parent.getChildCount());
     } catch (Throwable t) {
       handleException(parent, t);