Switch to downloaded SDK executable, drop executables in testing/bin.

tools/testing/dart/http_server.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 http_server;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'dart:convert' show
@@ skipping 154 matching lines @@
   Future startServers(String host, {int port: 0, int crossOriginPort: 0}) {
     return _startHttpServer(host, port: port).then((server) {
       _server = server;
       return _startHttpServer(host,
                               port: crossOriginPort,
                               allowedPort:_serverList[0].port);
     });
   }
 
   String httpServerCommandline() {
-    var dart = TestUtils.dartTestExecutable.toNativePath();
+    var dart = Platform.resolvedExecutable;
     var dartDir = TestUtils.dartDir;
     var script = dartDir.join(new Path("tools/testing/dart/http_server.dart"));
     var buildDirectory = _buildDirectory.toNativePath();
     var csp = useContentSecurityPolicy ? '--csp ' : '';
     return '$dart $script -p $port -c $crossOriginPort $csp'
            '--build-directory=$buildDirectory --runtime=$runtime '
            '--package-root=$_packageRoot';
   }
 
   void stopServers() {
@@ skipping 276 matching lines @@
 class _Entry implements Comparable {
   final String name;
   final String displayName;
 
   _Entry(this.name, this.displayName);
 
   int compareTo(_Entry other) {
     return name.compareTo(other.name);
   }
 }