Issue description:

I am using the flutter_isolate package to spawn an isolate. When I try to call getApplicationDocumentsDirectory() in the isolate I get the following error.

Unhandled Exception: MissingPluginException(No implementation found for method getApplicationDocumentsDirectory on channel plugins.flutter.io/path_provider)

flutter doctor -v

[✓] Flutter (Channel beta, v1.14.6, on Mac OS X 10.15.3 19D76, locale en-AU)
• Flutter version 1.14.6 at /Users/drkstr/development/flutter
• Framework revision fabeb2a (5 weeks ago), 2020-01-28 07:56:51 -0800
• Engine revision c4229bf
• Dart version 2.8.0 (build 2.8.0-dev.5.0 fc3af737c7)

[✓] Android toolchain - develop for Android devices (Android SDK version 29.0.2)

• Android SDK at /Users/drkstr/Library/Android/sdk
• Android NDK location not configured (optional; useful for native profiling support)
• Platform android-29, build-tools 29.0.2
• ANDROID_HOME = /Users/drkstr/Android/Sdk
• Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
• Java version OpenJDK Runtime Environment (build 1.8.0_202-release-1483-b49-5587405)
• All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 11.3.1)

• Xcode at /Applications/Xcode.app/Contents/Developer
• Xcode 11.3.1, Build version 11C504
• CocoaPods version 1.8.4

[✓] Chrome - develop for the web

• Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 3.5)

• Android Studio at /Applications/Android Studio.app/Contents
• Flutter plugin version 43.0.1
• Dart plugin version 191.8593
• Java version OpenJDK Runtime Environment (build 1.8.0_202-release-1483-b49-5587405)

[!] VS Code (version 1.42.1)

• VS Code at /Applications/Visual Studio Code.app/Contents
✗ Flutter extension not installed; install from
  https://marketplace.visualstudio.com/items?itemName=Dart-Code.flutter

[✓] Connected device (3 available)

• Pixel XL   • HT74T0205374 • android-arm64  • Android 10 (API 29)
• Chrome     • chrome       • web-javascript • Google Chrome 80.0.3987.122
• Web Server • web-server   • web-javascript • Flutter Tools

! Doctor found issues in 1 category.

pubspec.yaml file

name: tablet_tests
description: Application to test tablet functionality
version: 1.0.0+1

environment:
sdk: ">=2.1.0 <3.0.0"

dependencies:
flutter:
sdk: flutter
cupertino_icons: ^0.1.3
usb_serial: 0.2.3
flutter_isolate: 1.0.0+11
provider: 4.0.1
flutter_secure_storage: 3.3.1+1
sqflite: 1.2.0
path_provider: 1.6.1
path: 1.6.4

dev_dependencies:
flutter_test:
sdk: flutter

flutter:
uses-material-design: true

stacktrace

E/flutter (11692): [ERROR:flutter/lib/ui/ui_dart_state.cc(157)] Unhandled Exception: MissingPluginException(No implementation found for method getApplicationDocumentsDirectory on channel plugins.flutter.io/path_provider)
E/flutter (11692): #0 MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:154:7)
E/flutter (11692):
E/flutter (11692): #1 MethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart:329:12)
E/flutter (11692): #2 getApplicationDocumentsDirectory (package:path_provider/path_provider.dart:92:22)
E/flutter (11692): #3 DatabaseSingleton.initDB (package:tablet_tests/singletons/DatabaseSingleton.dart:31:42)
E/flutter (11692): #4 DatabaseSingleton.database (package:tablet_tests/singletons/DatabaseSingleton.dart:25:36)
E/flutter (11692): #5 DatabaseSingleton.insertLog (package:tablet_tests/singletons/DatabaseSingleton.dart:40:22)
E/flutter (11692): #6 backgroundTask (package:tablet_tests/background_processes/BackgroundStuff.dart:11:8)
E/flutter (11692): #7 isolate1 (package:tablet_tests/main.dart:10:3)
E/flutter (11692): #8 FlutterIsolate._isolateInitialize.. (package:flutter_isolate/flutter_isolate.dart:128:23)
E/flutter (11692): #9 _rootRunUnary (dart:async/zone.dart:1138:13)
E/flutter (11692): #10 _CustomZone.runUnary (dart:async/zone.dart:1031:19)
E/flutter (11692): #11 _CustomZone.runUnaryGuarded (dart:async/zone.dart:933:7)
E/flutter (11692): #12 _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:339:11)
E/flutter (11692): #13 _BufferingStreamSubscription._add (dart:async/stream_impl.dart:266:7)
E/flutter (11692): #14 _SyncStreamControllerDispatch._sendData (dart:async/stream_controller.dart:773:19)
E/flutter (11692): #15 _StreamController._add (dart:async/stream_controller.dart:649:7)
E/flutter (11692): #16 _StreamController.add (dart:async/stream_controller.dart:595:5)
E/flutter (11692): #17 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:168:12)

The output of flutter run --verbose:
https://drive.google.com/open?id=1heTLOyNBqSR13jv8MzLOj6sb2whjEQcK01KbRnxHzz4

Minimal app to reproduce the error:
https://drive.google.com/open?id=1eWJguDVGzyeuzvhReQVHb1i8uIEmSX6A

To reproduce the error download and run the minimal app I have linked above.

Let me know if you would like any more info.