Support `shadowView.rootView`

Reviewed By: shergin

Differential Revision: D5418509

fbshipit-source-id: 585b088678096ccf8416ea21a675d8953bfa82c8

React/Views/RCTShadowView+Hierarchy.h

@@ -0,0 +1,16 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+#import <React/RCTRootShadowView.h>
+#import <React/RCTShadowView.h>
+
+@interface RCTShadowView (Hierarchy)
+
+@property (nonatomic, readonly) RCTRootShadowView *rootView;
+
+@end

React/Views/RCTShadowView+Hierarchy.m

@@ -0,0 +1,23 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+#import "RCTShadowView+Hierarchy.h"
+
+@implementation RCTShadowView (Hierarchy)
+
+- (nullable RCTRootShadowView *)rootView
+{
+  RCTShadowView *view = self;
+  while (view != nil && ![view isKindOfClass:[RCTRootShadowView class]]) {
+    view = view.superview;
+  }
+
+  return (RCTRootShadowView *)view;
+}
+
+@end