Fix more strong mode errors and warnings.

lib/src/git.dart

 // Copyright (c) 2012, 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.
 
 /// Helper functionality for invoking Git.
 import 'dart:async';
 import 'dart:io';
 
 import 'package:stack_trace/stack_trace.dart';
 
@@ skipping 24 matching lines @@
   _isInstalledCache = command != null;
   return _isInstalledCache;
 }
 bool _isInstalledCache;
 
 /// Run a git process with [args] from [workingDir].
 ///
 /// Returns the stdout as a list of strings if it succeeded. Completes to an
 /// exception if it failed.
 Future<List<String>> run(List<String> args,
-    {String workingDir, Map<String, String> environment}) {
+    {String workingDir, Map<String, String> environment}) async {
   if (!isInstalled) {
     fail("Cannot find a Git executable.\n"
         "Please ensure Git is correctly installed.");
   }
 
   log.muteProgress();
-  return runProcess(command, args, workingDir: workingDir,
-      environment: environment).then((result) {
+  try {
+    var result = await runProcess(command, args, workingDir: workingDir,
+        environment: environment);
     if (!result.success) throw new GitException(args, result.stderr.join("\n"));
-
     return result.stdout;
-  }).whenComplete(() {
+  } finally {
     log.unmuteProgress();
-  });
+  }
 }
 
 /// Like [run], but synchronous.
 List<String> runSync(List<String> args, {String workingDir,
     Map<String, String> environment}) {
   if (!isInstalled) {
     fail("Cannot find a Git executable.\n"
         "Please ensure Git is correctly installed.");
   }
 
@@ skipping 42 matching lines @@
     var result = runProcessSync(command, ["--version"]);
     var regexp = new RegExp("^git version");
     return result.stdout.length == 1 && regexp.hasMatch(result.stdout.single);
   } on ProcessException catch (error, stackTrace) {
     var chain = new Chain.forTrace(stackTrace);
     // If the process failed, they probably don't have it.
     log.error('Git command is not "$command": $error\n$chain');
     return false;
   }
 }