Migrate scrollResponderScrollNativeHandleToKeyboard function to take nativeRef

Summary:
We need to get rid of findNodeHandle calls so migrating scrollResponderScrollNativeHandleToKeyboard to take a ref to a host component.

I made this change with Flow, and tested by rendering UserJobApplicationForm

Reviewed By: mdvacca

Differential Revision: D17099280

fbshipit-source-id: 96af692006aace2c206f268f5416984b00f8a438

Libraries/Components/TextInput/TextInput.js

@@ -904,6 +904,12 @@ const TextInput = createReactClass({
     this._inputRef = ref;
   },
 
+  getNativeRef: function(): ?React.ElementRef<
+    Class<ReactNative.NativeComponent<mixed>>,
+  > {
+    return this._inputRef;
+  },
+
   _renderIOSLegacy: function() {
     let textContainer;
 
@@ -1227,6 +1233,10 @@ const TextInput = createReactClass({
 class InternalTextInputType extends ReactNative.NativeComponent<Props> {
   clear() {}
 
+  getNativeRef(): ?React.ElementRef<
+    Class<ReactNative.NativeComponent<mixed>>,
+  > {}
+
   // $FlowFixMe
   isFocused(): boolean {}
 }