Fix status bar default on Android

Summary: On Android, the status bar color is not always black by default. The existing code causes the status bar to revert to black once the last `<StatusBar>` component is unmounted from the "stack". This diff reverts the bar background color to what it was before, instead of assuming black.

Reviewed By: yungsters

Differential Revision: D13368136

fbshipit-source-id: ef0154f776607b57bb9400b72d521f5f485b0075

Libraries/Components/StatusBar/StatusBar.js

@@ -198,7 +198,10 @@ class StatusBar extends React.Component<Props> {
   static _defaultProps = createStackEntry({
     animated: false,
     showHideTransition: 'fade',
-    backgroundColor: 'black',
+    backgroundColor: Platform.select({
+      android: StatusBarManager.DEFAULT_BACKGROUND_COLOR ?? 'black',
+      ios: 'black',
+    }),
     barStyle: 'default',
     translucent: false,
     hidden: false,

ReactAndroid/src/main/java/com/facebook/react/modules/statusbar/StatusBarModule.java

@@ -38,6 +38,7 @@
 public class StatusBarModule extends ReactContextBaseJavaModule {
 
   private static final String HEIGHT_KEY = "HEIGHT";
+  private static final String DEFAULT_BACKGROUND_COLOR_KEY = "DEFAULT_BACKGROUND_COLOR";
   public static final String NAME = "StatusBarManager";
 
   public StatusBarModule(ReactApplicationContext reactContext) {
@@ -52,14 +53,22 @@ public String getName() {
   @Override
   public @Nullable Map<String, Object> getConstants() {
     final Context context = getReactApplicationContext();
+    final Activity activity = getCurrentActivity();
+
     final int heightResId = context.getResources()
       .getIdentifier("status_bar_height", "dimen", "android");
     final float height = heightResId > 0 ?
       PixelUtil.toDIPFromPixel(context.getResources().getDimensionPixelSize(heightResId)) :
       0;
+    String statusBarColorString = "black";
+
+    if (activity != null && Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
+      final int statusBarColor = activity.getWindow().getStatusBarColor();
+      statusBarColorString = String.format("#%06X", (0xFFFFFF & statusBarColor));
+    }
 
     return MapBuilder.<String, Object>of(
-      HEIGHT_KEY, height);
+      HEIGHT_KEY, height, DEFAULT_BACKGROUND_COLOR_KEY, statusBarColorString);
   }
 
   @ReactMethod