Introducing `-[RCTUIManager shadowViewForReactTag:]`

Reviewed By: javache

Differential Revision: D5042093

fbshipit-source-id: 7c154b660f51de6d575f3c4a70321415512e92a2

React/Modules/RCTUIManager.h

@@ -81,6 +81,11 @@ RCT_EXTERN NSString *const RCTUIManagerRootViewKey;
  */
 - (UIView *)viewForReactTag:(NSNumber *)reactTag;
 
+/**
+ * Gets the shadow view associated with a reactTag.
+ */
+- (RCTShadowView *)shadowViewForReactTag:(NSNumber *)reactTag;
+
 /**
  * Set the available size (`availableSize` property) for a root view.
  * This might be used in response to changes in external layout constraints.

React/Modules/RCTUIManager.m

@@ -409,6 +409,12 @@ BOOL RCTIsUIManagerQueue()
   return _viewRegistry[reactTag];
 }
 
+- (RCTShadowView *)shadowViewForReactTag:(NSNumber *)reactTag
+{
+  RCTAssertUIManagerQueue();
+  return _shadowViewRegistry[reactTag];
+}
+
 - (void)setAvailableSize:(CGSize)availableSize forRootView:(UIView *)rootView
 {
   RCTAssertMainQueue();