Migrate pub away from throwing strings.

utils/pub/http.dart

 // Copyright (c) 2012, 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.
 
 /// Helpers for dealing with HTTP.
 library pub.http;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:json' as json;
@@ skipping 51 matching lines @@
         throw new PubHttpException(response);
       });
     }).catchError((error) {
       if (error is SocketIOException &&
           error.osError != null) {
         if (error.osError.errorCode == 8 ||
             error.osError.errorCode == -2 ||
             error.osError.errorCode == -5 ||
             error.osError.errorCode == 11001 ||
             error.osError.errorCode == 11004) {
-          throw 'Could not resolve URL "${request.url.origin}".';
+          throw new UserFacingException('Could not resolve URL '
+              '"${request.url.origin}".');
         } else if (error.osError.errorCode == -12276) {
-          throw 'Unable to validate SSL certificate for '
-              '"${request.url.origin}".';
+          throw new UserFacingException('Unable to validate SSL certificate '
+              'for "${request.url.origin}".');
         }
       }
       throw error;
     }), HTTP_TIMEOUT, 'fetching URL "${request.url}"');
   }
 
   /// Logs the fact that [request] was sent, and information about it.
   void _logRequest(http.BaseRequest request) {
     var requestLog = new StringBuffer();
     requestLog.writeln("HTTP ${request.method} ${request.url}");
@@ skipping 95 matching lines @@
   } catch (e) {
     // TODO(nweiz): narrow this catch clause once issue 6775 is fixed.
     invalidServerResponse(response);
   }
   if (value is! Map) invalidServerResponse(response);
   return value;
 }
 
 /// Throws an error describing an invalid response from the server.
 void invalidServerResponse(http.Response response) {
-  throw 'Invalid server response:\n${response.body}';
+  throw new UserFacingException('Invalid server response:\n${response.body}');
 }
 
 /// Exception thrown when an HTTP operation fails.
 class PubHttpException implements Exception {
   final http.Response response;
 
   const PubHttpException(this.response);
 
   String toString() => 'HTTP error ${response.statusCode}: '
       '${response.reasonPhrase}';
 }