Helps to add the new files

script/tool/lib/src/common/pub_utils.dart

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+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:io' as io;
+
+import 'package:platform/platform.dart';
+
+import 'process_runner.dart';
+import 'repository_package.dart';
+
+/// Runs either `dart pub get` or `flutter pub get` in [package], depending on
+/// the package type.
+///
+/// If [alwaysUseFlutter] is true, it will use `flutter pub get` regardless.
+/// This can be useful, for instance, to get the `flutter`-default behavior
+/// of fetching example packages as well.
+///
+/// If [streamOutput] is false, output will only be printed if the command
+/// fails.
+Future<bool> runPubGet(
+    RepositoryPackage package, ProcessRunner processRunner, Platform platform,
+    {bool alwaysUseFlutter = false, bool streamOutput = true}) async {
+  // Running `dart pub get` on a Flutter package can fail if a non-Flutter Dart
+  // is first in the path, so use `flutter pub get` for any Flutter package.
+  final bool useFlutter = alwaysUseFlutter || package.requiresFlutter();
+  final String command =
+      useFlutter ? (platform.isWindows ? 'flutter.bat' : 'flutter') : 'dart';
+  final List<String> args = <String>['pub', 'get'];
+
+  final int exitCode;
+  if (streamOutput) {
+    exitCode = await processRunner.runAndStream(command, args,
+        workingDir: package.directory);
+  } else {
+    final io.ProcessResult result =
+        await processRunner.run(command, args, workingDir: package.directory);
+    exitCode = result.exitCode;
+    if (exitCode != 0) {
+      print('${result.stdout}\n${result.stderr}\n');
+    }
+  }
+  return exitCode == 0;
+}

script/tool/test/common/pub_utils_test.dart

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+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:file/file.dart';
+import 'package:file/memory.dart';
+import 'package:flutter_plugin_tools/src/common/pub_utils.dart';
+import 'package:test/test.dart';
+
+import '../mocks.dart';
+import '../util.dart';
+
+void main() {
+  late FileSystem fileSystem;
+  late Directory packagesDir;
+  late RecordingProcessRunner processRunner;
+
+  setUp(() {
+    fileSystem = MemoryFileSystem();
+    packagesDir = createPackagesDirectory(fileSystem: fileSystem);
+    processRunner = RecordingProcessRunner();
+  });
+
+  test('runs with Dart for a non-Flutter package by default', () async {
+    final RepositoryPackage package =
+        createFakePackage('a_package', packagesDir);
+    final MockPlatform platform = MockPlatform();
+
+    await runPubGet(package, processRunner, platform);
+
+    expect(
+        processRunner.recordedCalls,
+        orderedEquals(<ProcessCall>[
+          ProcessCall('dart', const <String>['pub', 'get'], package.path),
+        ]));
+  });
+
+  test('runs with Flutter for a Flutter package by default', () async {
+    final RepositoryPackage package =
+        createFakePackage('a_package', packagesDir, isFlutter: true);
+    final MockPlatform platform = MockPlatform();
+
+    await runPubGet(package, processRunner, platform);
+
+    expect(
+        processRunner.recordedCalls,
+        orderedEquals(<ProcessCall>[
+          ProcessCall('flutter', const <String>['pub', 'get'], package.path),
+        ]));
+  });
+
+  test('runs with Flutter for a Dart package when requested', () async {
+    final RepositoryPackage package =
+        createFakePackage('a_package', packagesDir);
+    final MockPlatform platform = MockPlatform();
+
+    await runPubGet(package, processRunner, platform, alwaysUseFlutter: true);
+
+    expect(
+        processRunner.recordedCalls,
+        orderedEquals(<ProcessCall>[
+          ProcessCall('flutter', const <String>['pub', 'get'], package.path),
+        ]));
+  });
+
+  test('uses the correct Flutter command on Windows', () async {
+    final RepositoryPackage package =
+        createFakePackage('a_package', packagesDir, isFlutter: true);
+    final MockPlatform platform = MockPlatform(isWindows: true);
+
+    await runPubGet(package, processRunner, platform);
+
+    expect(
+        processRunner.recordedCalls,
+        orderedEquals(<ProcessCall>[
+          ProcessCall(
+              'flutter.bat', const <String>['pub', 'get'], package.path),
+        ]));
+  });
+
+  test('reports success', () async {
+    final RepositoryPackage package =
+        createFakePackage('a_package', packagesDir);
+    final MockPlatform platform = MockPlatform();
+
+    final bool result = await runPubGet(package, processRunner, platform);
+
+    expect(result, true);
+  });
+
+  test('reports failure', () async {
+    final RepositoryPackage package =
+        createFakePackage('a_package', packagesDir);
+    final MockPlatform platform = MockPlatform();
+
+    processRunner.mockProcessesForExecutable['dart'] = <FakeProcessInfo>[
+      FakeProcessInfo(MockProcess(exitCode: 1), <String>['pub', 'get'])
+    ];
+
+    final bool result = await runPubGet(package, processRunner, platform);
+
+    expect(result, false);
+  });
+}