Fixed Flow typing of TextInput refs

Summary:
`React.ElementRef<HostComponent<mixed>>` is an inexact object type, which can not be spread into an exact object type, as is happening here. This error is masked in types-first mode, but causes the instance type of this component to be `any`. In a future version of Flow, this issue will be fixed, so this change unblocks upgrading Flow.

This change is likely to cause code using `TextInput` refs to find errors which were missed before.

Changelog:
[General][Fixed] - Fixed Flow typing of TextInput refs

Reviewed By: yungsters

Differential Revision: D26733314

fbshipit-source-id: 8aa26ce5b49357b279f76dd1767a17a9fb4dd4f1

Libraries/Lists/FlatList.js

@@ -373,6 +373,8 @@ class FlatList<ItemT> extends React.PureComponent<Props<ItemT>, void> {
     | ?React.ElementRef<typeof View>
     | ?React.ElementRef<ScrollViewNativeComponent> {
     if (this._listRef) {
+      /* $FlowFixMe[incompatible-return] Suppresses errors found when fixing
+       * TextInput typing */
       return this._listRef.getScrollRef();
     }
   }

Libraries/Renderer/shims/ReactNativeTypes.js

@@ -99,7 +99,7 @@ export type PartialViewConfig = $ReadOnly<{
   validAttributes?: PartialAttributeConfiguration,
 }>;
 
-export type NativeMethods = {
+export type NativeMethods = {|
   blur(): void,
   focus(): void,
   measure(callback: MeasureOnSuccessCallback): void,
@@ -110,8 +110,7 @@ export type NativeMethods = {
     onFail?: () => void,
   ): void,
   setNativeProps(nativeProps: {...}): void,
-  ...
-};
+|};
 
 export type HostComponent<T> = AbstractComponent<T, $ReadOnly<NativeMethods>>;