Add a function for finding the HTTP proxy server from environment variables

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 "dart:async";
 import "dart:io";
 import "dart:uri";
 
 class Server {
   HttpServer server;
@@ skipping 214 matching lines @@
           .then((HttpClientRequest clientRequest) {
             String content = "$i$i$i";
             clientRequest.write(content);
             return clientRequest.close();
           })
           .then((HttpClientResponse response) {
             response.listen((_) {}, onDone: () {
               testProxyDoneCount++;
               if (testProxyDoneCount == proxy.length * 2) {
                 Expect.equals(proxy.length, server.requestCount);
+                Expect.equals(proxy.length, secureServer.requestCount);
                 proxyServer.shutdown();
                 server.shutdown();
                 secureServer.shutdown();
                 client.close();
               }
             });
           });
       }
 
       test(false);
@@ skipping 59 matching lines @@
               client.close();
             }
           });
         });
     }
   });
   });
   });
 }
 
+int testProxyFromEnviromentDoneCount = 0;
+void testProxyFromEnviroment() {
+  setupProxyServer().then((proxyServer) {
+  setupServer(1).then((server) {
+  setupServer(1, secure: true).then((secureServer) {
+    HttpClient client = new HttpClient();
+
+    client.findProxy = (Uri uri) {
+      return HttpClient.findProxyFromEnvironment(
+          uri,
+          environment: {"http_proxy": "localhost:${proxyServer.port}",
+                        "https_proxy": "localhost:${proxyServer.port}"});
+    };
+
+    const int loopCount = 5;
+    for (int i = 0; i < loopCount; i++) {
+      test(bool secure) {
+        String url = secure
+            ? "https://localhost:${secureServer.port}/$i"
+            : "http://127.0.0.1:${server.port}/$i";
+
+        client.postUrl(Uri.parse(url))
+          .then((HttpClientRequest clientRequest) {
+            String content = "$i$i$i";
+            clientRequest.write(content);
+            return clientRequest.close();
+          })
+          .then((HttpClientResponse response) {
+            response.listen((_) {}, onDone: () {
+              testProxyFromEnviromentDoneCount++;
+              if (testProxyFromEnviromentDoneCount == loopCount * 2) {
+                Expect.equals(loopCount, server.requestCount);
+                Expect.equals(loopCount, secureServer.requestCount);
+                proxyServer.shutdown();
+                server.shutdown();
+                secureServer.shutdown();
+                client.close();
+              }
+            });
+          });
+      }
+
+      test(false);
+      test(true);
+    }
+  });
+  });
+  });
+}
+
 int testRealProxyDoneCount = 0;
 void testRealProxy() {
   setupServer(1).then((server) {
     HttpClient client = new HttpClient();
 
     List<String> proxy =
         ["PROXY localhost:8080",
          "PROXY localhost:8080; PROXY hede.hule.hest:8080",
          "PROXY hede.hule.hest:8080; PROXY localhost:8080",
          "PROXY localhost:8080; DIRECT"];
@@ skipping 32 matching lines @@
   SecureSocket.initialize(database: testPkcertDatabase.toNativePath(),
                           password: 'dartdart');
 }
 
 main() {
   InitializeSSL();
   testInvalidProxy();
   testDirectProxy();
   testProxy();
   testProxyChain();
+  testProxyFromEnviroment();
   // This test is not normally run. It can be used for locally testing
   // with a real proxy server (e.g. Apache).
   //testRealProxy();
 }