Start using the proxy resolve IPC for plugins....

chrome/common/render_messages_internal.h

 // Copyright (c) 2006-2008 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.
 
 // This header is meant to be included in multiple passes, hence no traditional
 // header guard.
 // See ipc_message_macros.h for explanation of the macros and passes.
 
 #include <string>
 #include <vector>
@@ skipping 1084 matching lines @@
                              gfx::NativeViewId /* window */,
                              gfx::Rect /* Out: Window location */)
 
   // Queries the browser for suggestion for autofill in a form input field.
   IPC_MESSAGE_ROUTED4(ViewHostMsg_QueryFormFieldAutofill,
                       std::wstring /* field name */,
                       std::wstring /* user entered text */,
                       int64 /* id of the text input field */,
                       int /* id of this message */)
 
+  // Get the list of proxies to use for |url|, as a semicolon delimited list
+  // of "<TYPE> <HOST>:<PORT>" | "DIRECT". See also
+  // PluginProcessHostMsg_ResolveProxy which does the same thing.
+  IPC_SYNC_MESSAGE_CONTROL1_2(ViewHostMsg_ResolveProxy,
+                              GURL /* url */,
+                              int /* network error */,
+                              std::string /* proxy list */)
+
 IPC_END_MESSAGES(ViewHost)