Another attempt at landing this patch....

chrome/plugin/webplugin_proxy.cc

 // Copyright (c) 2009 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.
 
 #include "chrome/plugin/webplugin_proxy.h"
 
 #include "build/build_config.h"
 #if defined(OS_LINUX)
 #include <gtk/gtk.h>
 #endif
@@ skipping 269 matching lines @@
   return cp_browsing_context_;
 }
 
 WebPluginProxy* WebPluginProxy::FromCPBrowsingContext(
     CPBrowsingContext context) {
   return GetContextMap()[context];
 }
 
 WebPluginResourceClient* WebPluginProxy::GetResourceClient(int id) {
   ResourceClientMap::iterator iterator = resource_clients_.find(id);
+  // The IPC messages which deal with streams are now asynchronous. It is
+  // now possible to receive stream messages from the renderer for streams
+  // which may have been cancelled by the plugin.
   if (iterator == resource_clients_.end()) {
-    NOTREACHED();
     return NULL;
   }
 
   return iterator->second;
 }
 
 int WebPluginProxy::GetRendererProcessId() {
   if (channel_.get())
     return channel_->peer_pid();
   return 0;
@@ skipping 344 matching lines @@
                                               const char* range_info,
                                               intptr_t existing_stream,
                                               bool notify_needed,
                                               intptr_t notify_data) {
 
   Send(new PluginHostMsg_InitiateHTTPRangeRequest(route_id_, url,
                                                   range_info, existing_stream,
                                                   notify_needed, notify_data));
 }
 
+void WebPluginProxy::SetDeferResourceLoading(int resource_id, bool defer) {
+  Send(new PluginHostMsg_DeferResourceLoading(route_id_, resource_id, defer));
+}
+
 void WebPluginProxy::OnPaint(const gfx::Rect& damaged_rect) {
   child_process_logging::ScopedActiveURLSetter url_setter(page_url_);
 
   Paint(damaged_rect);
   Send(new PluginHostMsg_InvalidateRect(route_id_, damaged_rect));
 }
 
 bool WebPluginProxy::IsOffTheRecord() {
   return channel_->off_the_record();
 }
 
 void WebPluginProxy::ResourceClientDeleted(
     WebPluginResourceClient* resource_client) {
   ResourceClientMap::iterator index = resource_clients_.begin();
   while (index != resource_clients_.end()) {
     WebPluginResourceClient* client = (*index).second;
 
     if (client == resource_client) {
       resource_clients_.erase(index++);
     } else {
       index++;
     }
   }
 }