Back out "[react-native][PR] Remove the deprecated isIPhoneX_deprecated constant"

Summary:
Original commit changeset: 0b0b3a2d7b80

Reverting D8714400 which removed the `isIPhoneX_deprecated` flag, which is still widely used across the RN codebase https://fburl.com/biggrep/16jg5bzn

Reviewed By: hramos

Differential Revision: D8743401

fbshipit-source-id: cfc44bdd8019eda41e67ca573b20be417d121d12

RNTester/js/SafeAreaViewExample.js

@@ -64,6 +64,21 @@ class SafeAreaViewExample extends React.Component<
   }
 }
 
+class IsIPhoneXExample extends React.Component<{}> {
+  render() {
+    return (
+      <View>
+        <Text>
+          Is this an iPhone X:{' '}
+          {DeviceInfo.isIPhoneX_deprecated
+            ? 'Yeah!'
+            : 'Nope. (Or `isIPhoneX_deprecated` was already removed.)'}
+        </Text>
+      </View>
+    );
+  }
+}
+
 exports.examples = [
   {
     title: '<SafeAreaView> Example',
@@ -71,6 +86,15 @@ exports.examples = [
       'SafeAreaView automatically applies paddings reflect the portion of the view that is not covered by other (special) ancestor views.',
     render: () => <SafeAreaViewExample />,
   },
+  {
+    title: 'isIPhoneX_deprecated Example',
+    description:
+      '`DeviceInfo.isIPhoneX_deprecated` returns true only on iPhone X. ' +
+      'Note: This prop is deprecated and will be removed right after June 01, 2018. ' +
+      'Please use this only for a quick and temporary solution. ' +
+      'Use <SafeAreaView> instead.',
+    render: () => <IsIPhoneXExample />,
+  },
 ];
 
 var styles = StyleSheet.create({

React/Modules/RCTDeviceInfo.m

@@ -51,6 +51,22 @@ RCT_EXPORT_MODULE()
 #endif
 }
 
+static BOOL RCTIsIPhoneX() {
+  static BOOL isIPhoneX = NO;
+  static dispatch_once_t onceToken;
+
+  dispatch_once(&onceToken, ^{
+    RCTAssertMainQueue();
+
+    isIPhoneX = CGSizeEqualToSize(
+      [UIScreen mainScreen].nativeBounds.size,
+      CGSizeMake(1125, 2436)
+    );
+  });
+
+  return isIPhoneX;
+}
+
 static NSDictionary *RCTExportedDimensions(RCTBridge *bridge)
 {
   RCTAssertMainQueue();
@@ -86,6 +102,11 @@ static NSDictionary *RCTExportedDimensions(RCTBridge *bridge)
 {
   return @{
     @"Dimensions": RCTExportedDimensions(_bridge),
+    // Note:
+    // This prop is deprecated and will be removed right after June 01, 2018.
+    // Please use this only for a quick and temporary solution.
+    // Use <SafeAreaView> instead.
+    @"isIPhoneX_deprecated": @(RCTIsIPhoneX()),
   };
 }