Adding new styling props to FlatList/VirtualizedList for ListHeaderComponent and ListFooterComponent

Summary:
We ran into a problem trying to style the optional prop `ListHeaderComponent` in the `FlatList` library component. Essentially we wanted to make `ListHeaderComponent` a flex item that filled all of the empty space in the list if there was any. Unfortunately the `ListHeaderComponent` is later wrapped in a `View` that blocked our styling. The `View` component was necessary as it added styling to handle inverting the `FlatList`. Similarly `ListFooterComponent` was handled the same way.

We came up the simple solution of adding two new optional props, `ListHeaderComponentStyle` and `ListFooterComponentStyle`, that are of type `ViewStyleProp` that allow users to pass in styling for `ListHeaderComponent` and `ListFooterComponent`.

With this change we were able to do something like the following to get the header component to fill all empty space in the `FlatList`.

```
<FlatList
    ...
    contentContainerStyle={{flexGrow: 1}}
    ListHeaderComponent={<View style={{flex: 1}} />}
    ListHeaderComponentStyle={{flexGrow: 1}}
    ...
/>
```
This solution will give users a lot more freedom when working with headers and footers.

Reviewed By: sahrens

Differential Revision: D8777038

fbshipit-source-id: f34116ce68548ea70223e639d0f84a099327f6b3

Libraries/Lists/FlatList.js

@@ -18,7 +18,7 @@ const StyleSheet = require('StyleSheet');
 
 const invariant = require('fbjs/lib/invariant');
 
-import type {DangerouslyImpreciseStyleProp} from 'StyleSheet';
+import type {DangerouslyImpreciseStyleProp, ViewStyleProp} from 'StyleSheet';
 import type {
   ViewabilityConfig,
   ViewToken,
@@ -88,11 +88,19 @@ type OptionalProps<ItemT> = {
    * a rendered element.
    */
   ListFooterComponent?: ?(React.ComponentType<any> | React.Element<any>),
+  /**
+   * Styling for internal View for ListFooterComponent
+   */
+  ListFooterComponentStyle?: ViewStyleProp,
   /**
    * Rendered at the top of all the items. Can be a React Component Class, a render function, or
    * a rendered element.
    */
   ListHeaderComponent?: ?(React.ComponentType<any> | React.Element<any>),
+  /**
+   * Styling for internal View for ListHeaderComponent
+   */
+  ListHeaderComponentStyle?: ViewStyleProp,
   /**
    * Optional custom style for multi-item rows generated when numColumns > 1.
    */

Libraries/Lists/VirtualizedList.js

@@ -31,7 +31,7 @@ const warning = require('fbjs/lib/warning');
 
 const {computeWindowedRenderLimits} = require('VirtualizeUtils');
 
-import type {DangerouslyImpreciseStyleProp} from 'StyleSheet';
+import type {DangerouslyImpreciseStyleProp, ViewStyleProp} from 'StyleSheet';
 import type {
   ViewabilityConfig,
   ViewToken,
@@ -124,11 +124,19 @@ type OptionalProps = {
    * a rendered element.
    */
   ListFooterComponent?: ?(React.ComponentType<any> | React.Element<any>),
+  /**
+   * Styling for internal View for ListFooterComponent
+   */
+  ListFooterComponentStyle?: ViewStyleProp,
   /**
    * Rendered at the top of all the items. Can be a React Component Class, a render function, or
    * a rendered element.
    */
   ListHeaderComponent?: ?(React.ComponentType<any> | React.Element<any>),
+  /**
+   * Styling for internal View for ListHeaderComponent
+   */
+  ListHeaderComponentStyle?: ViewStyleProp,
   /**
    * A unique identifier for this list. If there are multiple VirtualizedLists at the same level of
    * nesting within another VirtualizedList, this key is necessary for virtualization to
@@ -756,7 +764,12 @@ class VirtualizedList extends React.PureComponent<Props, State> {
         <VirtualizedCellWrapper
           cellKey={this._getCellKey() + '-header'}
           key="$header">
-          <View onLayout={this._onLayoutHeader} style={inversionStyle}>
+          <View
+            onLayout={this._onLayoutHeader}
+            style={StyleSheet.compose(
+              inversionStyle,
+              this.props.ListHeaderComponentStyle,
+            )}>
             {
               // $FlowFixMe - Typing ReactNativeComponent revealed errors
               element
@@ -892,7 +905,12 @@ class VirtualizedList extends React.PureComponent<Props, State> {
         <VirtualizedCellWrapper
           cellKey={this._getCellKey() + '-footer'}
           key="$footer">
-          <View onLayout={this._onLayoutFooter} style={inversionStyle}>
+          <View
+            onLayout={this._onLayoutFooter}
+            style={StyleSheet.compose(
+              inversionStyle,
+              this.props.ListFooterComponentStyle,
+            )}>
             {
               // $FlowFixMe - Typing ReactNativeComponent revealed errors
               element

Libraries/Lists/__tests__/__snapshots__/FlatList-test.js.snap

@@ -60,7 +60,6 @@ exports[`FlatList renders all the bells and whistles 1`] = `
   <View>
     <View
       onLayout={[Function]}
-      style={null}
     >
       <header />
     </View>
@@ -119,7 +118,6 @@ exports[`FlatList renders all the bells and whistles 1`] = `
     </View>
     <View
       onLayout={[Function]}
-      style={null}
     >
       <footer />
     </View>

Libraries/Lists/__tests__/__snapshots__/SectionList-test.js.snap

@@ -341,7 +341,6 @@ exports[`SectionList renders all the bells and whistles 1`] = `
   <View>
     <View
       onLayout={[Function]}
-      style={null}
     >
       <header
         v=""
@@ -484,7 +483,6 @@ exports[`SectionList renders all the bells and whistles 1`] = `
     </View>
     <View
       onLayout={[Function]}
-      style={null}
     >
       <footer
         v=""

Libraries/Lists/__tests__/__snapshots__/VirtualizedList-test.js.snap

@@ -665,14 +665,12 @@ exports[`VirtualizedList renders empty list with empty component 1`] = `
   <View>
     <View
       onLayout={[Function]}
-      style={null}
     >
       <header />
     </View>
     <empty />
     <View
       onLayout={[Function]}
-      style={null}
     >
       <footer />
     </View>