Add support for ProxyResolverErrorObserver to ProxyResolverMojo.

net/interfaces/proxy_resolver_service.mojom

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Put Mojo definitions into their own namespace to avoid collisions with C++
 // definitions.
 // TODO(amistry): Resolve the conflict between these two sets of definitions.
 module net.interfaces;
 
 import "host_resolver_service.mojom";
@@ skipping 24 matching lines @@
   // client.
   // TODO(amistry): Add BoundNetLog.
   GetProxyForUrl(string url, ProxyResolverRequestClient client);
 };
 
 interface ProxyResolverRequestClient {
   ReportResult(int32 error, array<ProxyServer>? proxy_servers);
   LoadStateChanged(int32 load_state);
 };
 
+interface ProxyResolverErrorObserver {
+  OnPacScriptError(int32 line_number, string error);
+};
+
 interface ProxyResolverFactory {
-  // TODO(amistry): Add NetLog and ProxyResolverErrorObserver.
+  // TODO(amistry): Add NetLog.
   CreateResolver(string pac_script,
                  ProxyResolver& resolver,
                  HostResolver host_resolver,
+                 ProxyResolverErrorObserver? error_observer,
                  ProxyResolverFactoryRequestClient client);
 };
 
 interface ProxyResolverFactoryRequestClient {
   ReportResult(int32 error);
 };