Define type signature for react-native-implementation

Summary: Explicitly define the types of the getters in `react-native-implementation` so we can enable Flow's types-first mode for that file.

Reviewed By: cpojer

Differential Revision: D16937607

fbshipit-source-id: 2e4cf483043a53c5407254ffa2b3211d40211019

.flowconfig

@@ -53,6 +53,9 @@ suppress_comment=\\(.\\|\n\\)*\\$FlowFixMe\\($\\|[^(]\\|(\\(<VERSION>\\)? *\\(si
 suppress_comment=\\(.\\|\n\\)*\\$FlowIssue\\((\\(<VERSION>\\)? *\\(site=[a-z,_]*react_native\\(_ios\\)?_\\(oss\\|fb\\)[a-z,_]*\\)?)\\)?:? #[0-9]+
 suppress_comment=\\(.\\|\n\\)*\\$FlowExpectedError
 
+experimental.well_formed_exports=true
+experimental.well_formed_exports.whitelist=<PROJECT_ROOT>/Libraries/react-native/react-native-implementation.js
+
 [lints]
 sketchy-null-number=warn
 sketchy-null-mixed=warn

.flowconfig.android

@@ -53,6 +53,9 @@ suppress_comment=\\(.\\|\n\\)*\\$FlowFixMe\\($\\|[^(]\\|(\\(<VERSION>\\)? *\\(si
 suppress_comment=\\(.\\|\n\\)*\\$FlowIssue\\((\\(<VERSION>\\)? *\\(site=[a-z,_]*react_native\\(_android\\)?_\\(oss\\|fb\\)[a-z,_]*\\)?)\\)?:? #[0-9]+
 suppress_comment=\\(.\\|\n\\)*\\$FlowExpectedError
 
+experimental.well_formed_exports=true
+experimental.well_formed_exports.whitelist=<PROJECT_ROOT>/Libraries/react-native/react-native-implementation.js
+
 [lints]
 sketchy-null-number=warn
 sketchy-null-mixed=warn

Libraries/Components/SafeAreaView/SafeAreaView.js

@@ -12,15 +12,14 @@ const Platform = require('../../Utilities/Platform');
 const React = require('react');
 const View = require('../View/View');
 
-import type {NativeComponent} from '../../Renderer/shims/ReactNative';
 import type {ViewProps} from '../View/ViewPropTypes';
 
 type Props = $ReadOnly<{|
   ...ViewProps,
   emulateUnlessSupported?: boolean,
 |}>;
 
-let exported: Class<React$Component<Props>> | Class<NativeComponent<Props>>;
+let exported: Class<React$Component<Props>>;
 
 /**
  * Renders nested content and automatically applies paddings reflect the portion
@@ -62,7 +61,7 @@ if (Platform.OS === 'android') {
 
   const SafeAreaViewRef = React.forwardRef(SafeAreaView);
   SafeAreaViewRef.displayName = 'SafeAreaView';
-  exported = ((SafeAreaViewRef: any): Class<NativeComponent<Props>>);
+  exported = ((SafeAreaViewRef: any): Class<React.Component<Props>>);
 }
 
 module.exports = exported;