Proper check for RCTRootShadowView in RCTUIManager

Summary: Because setting `intrinsicContentSize` for `RCTSurfaceRootView` doesn't have much sense.

Reviewed By: mmmulani

Differential Revision: D6701107

fbshipit-source-id: 259cdd27339bba3e8c9f98b6ca34affeb87f298c

Author: shergin

React/Modules/RCTUIManager.m

@@ -548,7 +548,10 @@ - (RCTViewManagerUIBlock)uiBlockWithLayoutUpdateForRootView:(RCTRootShadowView *
       });
     }
 
-    if (RCTIsReactRootView(reactTag)) {
+    if (
+        RCTIsReactRootView(reactTag) &&
+        [shadowView isKindOfClass:[RCTRootShadowView class]]
+    ) {
       CGSize contentSize = shadowView.frame.size;
 
       RCTExecuteOnMainQueue(^{