Fix analyzer warnings for browser_controller.

tools/testing/dart/browser_controller.dart

 // Copyright (c) 2013, 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.
 library browser;
 
 import "dart:async";
 import "dart:convert" show LineSplitter, UTF8, JSON;
 import "dart:core";
 import "dart:io";
 import "dart:math" show max, min;
@@ skipping 486 matching lines @@
 
 class SafariMobileSimulator extends Safari {
   /**
    * Directories where safari simulator stores state. We delete these if the
    * resetBrowserConfiguration is set
    */
   static const List<String> CACHE_DIRECTORIES = const [
     "Library/Application Support/iPhone Simulator/7.1/Applications"
   ];
 
+  // Helper function to delete many directories recursively.
+  Future<bool> deleteIfExists(Iterable<String> paths) async {
+    for (var path in paths) {
+      Directory directory = new Directory(path);
+      if (await directory.exists()) {
+        _logEvent("Deleting $path");
+        try {
+          await directory.delete(recursive: true);
+        } catch (error) {
+          _logEvent("Failure trying to delete $path: $error");
+          return false;
+        }
+      } else {
+        _logEvent("$path is not present");
+      }
+    }
+    return true;
+  }
+
   // Clears the cache if the static resetBrowserConfiguration flag is set.
   // Returns false if the command to actually clear the cache did not complete.
   Future<bool> resetConfiguration() {
     if (!Browser.resetBrowserConfiguration) return new Future.value(true);
     var home = Platform.environment['HOME'];
-    Iterator iterator = CACHE_DIRECTORIES.map((s) => "$home/$s").iterator;
-    return deleteIfExists(iterator);
+    var paths = CACHE_DIRECTORIES.map((s) => "$home/$s");
+    return deleteIfExists(paths);
   }
 
   Future<bool> start(String url) {
     _logEvent("Starting safari mobile simulator browser on: $url");
     return resetConfiguration().then((success) {
       if (!success) {
         _logEvent("Could not clear cache, exiting");
         return false;
       }
       var args = [
@@ skipping 371 matching lines @@
   static const Duration RESTART_BROWSER_INTERVAL = const Duration(seconds: 60);
 
   /// If the queue was recently empty, don't start another browser.
   static const Duration MIN_NONEMPTY_QUEUE_TIME = const Duration(seconds: 1);
 
   final Map configuration;
   final BrowserTestingServer testingServer;
 
   final String localIp;
   final String browserName;
-  final int maxNumBrowsers;
+  int maxNumBrowsers;
   final bool checkedMode;
   int numBrowsers = 0;
   // Used to send back logs from the browser (start, stop etc)
   Function logger;
 
   int browserIdCounter = 1;
 
   bool testingServerStarted = false;
   bool underTermination = false;
   int numBrowserGetTestTimeouts = 0;
@@ skipping 914 matching lines @@
     </div>
     <div id="embedded_iframe_div" class="test box">
       <iframe id="embedded_iframe"></iframe>
     </div>
   </body>
 </html>
 """;
     return driverContent;
   }
 }