Make Fuchsia tools Dart 2 clean (#19727)

packages/flutter_tools/bin/fuchsia_asset_builder.dart

@@ -6,6 +6,7 @@ import 'dart:async';
 
 import 'package:args/args.dart';
 import 'package:flutter_tools/src/asset.dart';
+import 'package:flutter_tools/src/base/context.dart';
 import 'package:flutter_tools/src/base/file_system.dart' as libfs;
 import 'package:flutter_tools/src/base/io.dart';
 import 'package:flutter_tools/src/base/platform.dart';
@@ -28,8 +29,8 @@ const List<String> _kRequiredOptions = <String>[
 ];
 
 Future<Null> main(List<String> args) {
-  return runInContext<Null>(() => run(args), overrides: <Type, dynamic>{
-    Usage: new DisabledUsage(),
+  return runInContext<Null>(() => run(args), overrides: <Type, Generator>{
+    Usage: () => new DisabledUsage(),
   });
 }
 

packages/flutter_tools/bin/fuchsia_tester.dart

@@ -6,6 +6,7 @@ import 'dart:async';
 
 import 'package:args/args.dart';
 import 'package:flutter_tools/src/base/common.dart';
+import 'package:flutter_tools/src/base/context.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/io.dart';
 import 'package:flutter_tools/src/cache.dart';
@@ -32,8 +33,8 @@ const String _kOptionCoverage = 'coverage';
 const String _kOptionCoveragePath = 'coverage-path';
 
 void main(List<String> args) {
-  runInContext<Null>(() => run(args), overrides: <Type, dynamic>{
-    Usage: new DisabledUsage(),
+  runInContext<Null>(() => run(args), overrides: <Type, Generator>{
+    Usage: () => new DisabledUsage(),
   });
 }
 

packages/flutter_tools/lib/src/context_runner.dart

@@ -37,7 +37,7 @@ import 'version.dart';
 
 Future<T> runInContext<T>(
   FutureOr<T> runner(), {
-  Map<Type, dynamic> overrides,
+  Map<Type, Generator> overrides,
 }) async {
   return await context.run<T>(
     name: 'global fallbacks',