Cleanup native view hierarchy when view is dropped.

Differential Revision: D2659738

fb-gh-sync-id: 1c14b8c3c6fabbd0e580777bb94221df6dd98f71

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

@@ -48,6 +48,12 @@ public abstract class ViewGroupManager <T extends ViewGroup>
     parent.removeViewAt(index);
   }
 
+  public void removeAllViews(T parent) {
+    for (int i = getChildCount(parent) - 1; i >= 0; i--) {
+      removeViewAt(parent, i);
+    }
+  }
+
   /**
    * Returns whether this View type needs to handle laying out its own children instead of
    * deferring to the standard css-layout algorithm.