Disallow mounting virtual nodes to Views

Summary: Virtual shadow nodes, such as RCTRawText, RCTTextInlineImage etc cannot be mounted to a View (ViewManager will throw an Exception if we ever try to). This diff is adding a check to make sure that Exception is never thrown.

Reviewed By: ahmedre

Differential Revision: D2800869

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

@@ -254,6 +254,10 @@ import com.facebook.react.uimanager.ViewProps;
   }
 
   /* package */ final void forceMountToView() {
+    if (isVirtual()) {
+      return;
+    }
+
     if (mDrawView == null) {
       mDrawView = DrawView.INSTANCE;
       if (getParent() != null) {