Fix per SDK Stream<Uint8List> breaking changes

This updates call sites with forward-compatible fixes for
a recent Dart SDK change that changed the following APIs
to be `Stream<Uint8List>` rather than `Stream<List<int>>`:

* HttpClientResponse
* File.openRead()

dart-lang/sdk#36900

Author: tvolkert

tool/grind.dart

@@ -46,7 +46,7 @@ colors() async {
   // Get color file from flutter.
   HttpClientRequest request = await new HttpClient().getUrl(Uri.parse(kUrl));
   HttpClientResponse response = await request.close();
-  List<String> data = await response.transform(utf8.decoder).toList();
+  List<String> data = await utf8.decoder.bind(response).toList();
 
   // Remove an import and define the Color class.
   String str = data.join('');

tool/icons/update_icons.dart

@@ -39,7 +39,7 @@ void main() async {
 Future<String> downloadUrl(String url) async {
   HttpClientRequest request = await new HttpClient().getUrl(Uri.parse(url));
   HttpClientResponse response = await request.close();
-  List<String> data = await response.transform(utf8.decoder).toList();
+  List<String> data = await utf8.decoder.bind(response).toList();
   return data.join('');
 }
 

tool/plugin/lib/plugin.dart

@@ -4,6 +4,7 @@
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
+import 'dart:typed_data';
 
 import 'package:args/args.dart';
 import 'package:args/command_runner.dart';
@@ -133,6 +134,7 @@ Future<File> genPluginXml(BuildSpec spec, String destDir, String path) async {
   dest.writeln();
   await new File(p.join(rootPath, 'resources', templatePath))
       .openRead()
+      .cast<List<int>>()
       .transform(utf8.decoder)
       .transform(new LineSplitter())
       .forEach((l) => dest.writeln(substituteTemplateVariables(l, spec)));