b/270298884

Follow the Android section of https://docs.flutter.dev/development/ui/navigation/deep-linking

If the deeplink is launched when the app is not open, it will launch with the default initial route / instead of the deeplinked route.

repro:

1. create a flutter app

import 'package:flutter/material.dart';

void main() => runApp(MaterialApp(
  routes: <String, WidgetBuilder> {
    '/': (_)=> Scaffold(appBar: AppBar(title: Text('/'))),
    '/abc': (_)=> Scaffold(appBar: AppBar(title: Text('/abc'))),
  }
));

2. in /android/app/src/main/AndroidManifest.xml, add following meta tags in

<meta-data android:name="flutter_deeplinking_enabled" android:value="true" />
<intent-filter android:autoVerify="true">
    <action android:name="android.intent.action.VIEW" />
    <category android:name="android.intent.category.DEFAULT" />
    <category android:name="android.intent.category.BROWSABLE" />
    <data android:scheme="http" android:host="flutterbooksample.com" />
    <data android:scheme="https" />
</intent-filter>

3. do a flutter run on any Android device (I am using motoG4)
4. force quit the app, and make sure the app is not in the background.
5. run adb command

adb shell 'am start -a android.intent.action.VIEW \
    -c android.intent.category.BROWSABLE \
    -d "http://flutterbooksample.com/abc"' \
    <package name>

expect: the page is opened with /abc in the appbar
actual: the page is opened with / in the appbar

This only happen if the app is started cold, if the app is in the background the deeplink command will work correctly.