pkg/test: Resolve a number of analyzer warnings

lib/src/runner/browser/content_shell.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. 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:async';
 import 'dart:convert';
 import 'dart:io';
 
 import '../../util/io.dart';
 import '../../utils.dart';
@@ skipping 87 matching lines @@
   /// Returns the full URL of the remote debugger for the host page.
   ///
   /// This takes the base remote debugger URL (which points to a browser-wide
   /// page) and uses its JSON API to find the resolved URL for debugging the
   /// host page.
   static Future<Uri> _getRemoteDebuggerUrl(Uri base) async {
     try {
       var client = new HttpClient();
       var request = await client.getUrl(base.resolve("/json/list"));
       var response = await request.close();
-      var json = await JSON.fuse(UTF8).decoder.bind(response).single;
+      var json = await JSON.fuse(UTF8).decoder.bind(response).single as List;

[nweiz, 2016/06/20 20:51:36]

Why doesn't this complain about calling operator [] on the result of json.first?

[kevmoo, 2016/06/20 20:57:49]

You get Object out of the fused decoder, which is not a List.

Each item in `List` is dynamic, though – so of course it has an index operator

       return base.resolve(json.first["devtoolsFrontendUrl"]);
     } catch (_) {
       // If we fail to talk to the remote debugger protocol, give up and return
       // the raw URL rather than crashing.
       return base;
     }
   }
 
   ContentShell._(Future<Process> startBrowser(), this.observatoryUrl,
           this.remoteDebuggerUrl)
       : super(startBrowser);
 
   /// Return the default executable for the current operating system.
   static String _defaultExecutable() =>
       Platform.isWindows ? "content_shell.exe" : "content_shell";
 }