Add 'uri' to HttpException, and include in toString.

sdk/lib/io/http.dart

Index: sdk/lib/io/http.dart
diff --git a/sdk/lib/io/http.dart b/sdk/lib/io/http.dart
index 09b7d8c9cf827e97b8e0c6f69a8b6360efaf0602..452dbe7cc4cfa1cc44e50af59b61776d390b4c58 100644
--- a/sdk/lib/io/http.dart
+++ b/sdk/lib/io/http.dart
@@ -1399,10 +1399,19 @@ abstract class DetachedSocket {
 
 class HttpException implements IOException {
   final String message;
-
-  const HttpException([String this.message = ""]);
-
-  String toString() => "HttpException: $message";
+  final Uri uri;
+
+  const HttpException(String this.message, {Uri this.uri});
+
+  String toString() {
+    var b = new StringBuffer();
+    b.write('HttpException: ');
+    b.write(message);
+    if (uri != null) {
+      b.write(', uri = $uri');
+    }
+    return b.toString();
+  }
 }