Fix all strong-mode errors and 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 10 matching lines @@
 ///
 /// Any errors starting or running the process are reported through [onExit].
 class ContentShell extends Browser {
   final name = "Content Shell";
 
   final Future<Uri> observatoryUrl;
 
   final Future<Uri> remoteDebuggerUrl;
 
   factory ContentShell(url, {String executable, bool debug: false}) {
-    var observatoryCompleter = new Completer.sync();
-    var remoteDebuggerCompleter = new Completer.sync();
+    var observatoryCompleter = new Completer<Uri>.sync();
+    var remoteDebuggerCompleter = new Completer<Uri>.sync();
     return new ContentShell._(() {
       if (executable == null) executable = _defaultExecutable();
 
-      tryPort([port]) async {
+      var tryPort = ([int port]) async {
         var args = ["--dump-render-tree", url.toString()];
         if (port != null) args.add("--remote-debugging-port=$port");
 
         var process = await Process.start(executable, args,
             environment: {"DART_FLAGS": "--checked"});
 
         if (debug) {
           observatoryCompleter.complete(lineSplitter.bind(process.stdout)
               .map((line) {
             var match = _observatoryRegExp.firstMatch(line);
@@ skipping 34 matching lines @@
 
         if (port != null) {
           remoteDebuggerCompleter.complete(
               _getRemoteDebuggerUrl(Uri.parse("http://localhost:$port")));
         } else {
           remoteDebuggerCompleter.complete(null);
         }
 
         stderr.cancel();
         return process;
-      }
+      };
 
       if (!debug) return tryPort();
-      return getUnusedPort(tryPort);
+      return getUnusedPort/*<Future<Process>>*/(tryPort);
     }, observatoryCompleter.future, remoteDebuggerCompleter.future);
   }
 
   /// 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 {
@@ skipping 10 matching lines @@
   }
 
   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";
 }