使用FlutterBoost展示platformView的时候会闪一下黑色

使用flutter原生的MaterialApp绑定到home上的话，这个platformView是有白色背景的；但是在使用FlutterBoost.init()展示的时候会闪一下黑色，在这个页面是白色背景的时候，会闪一下黑色，非常明显。

MaterialApp(
title: 'Flutter Demo',
builder: FlutterBoost.init(
builder: (BuildContext context, Widget child) => Container(
child: child,
color: Colors.white,
),
),
color: Colors.white,
navigatorObservers: [
FlutterExceptionNaviObserver()
],
home: MyPlatformView(),
),

FlutterBoost.singleton.registerPageBuilders({
'/': (pageName, params, _) => Container(),
'myPlatformView': (pageName, params, _) => MyPlatformView(),
});

Reproduce the flash using FlutterBoost.init() with a white-background MaterialApp and a platformView, then compare it with the direct home: MyPlatformView() setup. Start at the FlutterBoost.init() and registered myPlatformView entry points; done means the platformView no longer briefly shows a black background.

Written by the indexing model from the issue text.