fix analyzer failures

tests/standalone/io/http_proxy_test.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.
 
+import "package:convert/convert.dart";
 import "package:crypto/crypto.dart";
 import "package:expect/expect.dart";
-import "package:path/path.dart";
 import "dart:async";
 import "dart:io";
 import 'dart:convert';
 
 String localFile(path) => Platform.script.resolve(path).toFilePath();
 
 SecurityContext serverContext = new SecurityContext()
   ..useCertificateChain(localFile('certificates/server_chain.pem'))
   ..usePrivateKey(localFile('certificates/server_key.pem'),
                   password: 'dartdart');
@@ skipping 84 matching lines @@
   var nonce = "12345678";  // No need for random nonce in test.
 
   ProxyServer({this.ipV6: false}) : client = new HttpClient();
 
   void useBasicAuthentication(String username, String password) {
     this.username = username;
     this.password = password;
     authScheme = "Basic";
   }
 
-  void useDigestAuthentication(String username, String password) {
-    this.username = username;
-    this.password = password;
-    authScheme = "Digest";
-
-    // Calculate ha1.
-    var hasher = new MD5();
-    hasher.add("${username}:${realm}:${password}".codeUnits);
-    ha1 = CryptoUtils.bytesToHex(hasher.close());
-  }
-
   basicAuthenticationRequired(request) {
     request.fold(null, (x, y) {}).then((_) {
       var response = request.response;
       response.headers.set(HttpHeaders.PROXY_AUTHENTICATE,
                            "Basic, realm=$realm");
       response.statusCode = HttpStatus.PROXY_AUTHENTICATION_REQUIRED;
       response.close();
     });
   }
 
@@ skipping 66 matching lines @@
                 Expect.isNotNull(cnonce);
                 Expect.isNotNull(nc);
                 Expect.isFalse(ncs.contains(nc));
                 ncs.add(nc);
               } else {
                 Expect.isNull(cnonce);
                 Expect.isNull(nc);
               }
               Expect.isNotNull(header.parameters["response"]);
 
-              var hasher = new MD5();
-              hasher.add("${request.method}:${uri}".codeUnits);
-              var ha2 = CryptoUtils.bytesToHex(hasher.close());
+              var digest = md5.convert("${request.method}:${uri}".codeUnits);
+              var ha2 = hex.encode(digest.bytes);
 
-              var x;
-              hasher = new MD5();
               if (qop == null || qop == "" || qop == "none") {
-                hasher.add("$ha1:${nonce}:$ha2".codeUnits);
+                digest = md5.convert("$ha1:${nonce}:$ha2".codeUnits);
               } else {
-                hasher.add(
+                digest = md5.convert(
                     "$ha1:${nonce}:${nc}:${cnonce}:${qop}:$ha2".codeUnits);
               }
-              Expect.equals(CryptoUtils.bytesToHex(hasher.close()),
-                            header.parameters["response"]);
+              Expect.equals(hex.encode(digest.bytes),
+                  header.parameters["response"]);
 
               // Add a bogus Proxy-Authentication-Info for testing.
               var info = 'rspauth="77180d1ab3d6c9de084766977790f482", '
                          'cnonce="8f971178", '
                          'nc=000002c74, '
                          'qop=auth';
               request.response.headers.set("Proxy-Authentication-Info", info);
             }
           }
         }
@@ skipping 236 matching lines @@
   });
   });
 }
 
 main() {
   testInvalidProxy();
   testDirectProxy();
   testProxy();
   testProxyChain();
 }