net: Add namespace net to the remaining files under url_request directory.

chrome/browser/plugin_service.h

Index: chrome/browser/plugin_service.h
diff --git a/chrome/browser/plugin_service.h b/chrome/browser/plugin_service.h
index 8494fdab416b967b01cb3936d4134a0bbd454033..d24c4e20cff106ed8ef66df21e2d659c8e99ec12 100644
--- a/chrome/browser/plugin_service.h
+++ b/chrome/browser/plugin_service.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 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.
 
@@ -40,8 +40,10 @@ class Message;
 class MessageLoop;
 class Profile;
 class ResourceDispatcherHost;
-class URLRequestContext;
 
+namespace net {
+class URLRequestContext;
+}  // namespace net
 
 namespace webkit {
 namespace npapi {