Send replies to sync IPCs from swapped out renderers.

content/browser/renderer_host/render_view_host.cc

 // Copyright (c) 2012 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 "content/browser/renderer_host/render_view_host.h"
 
 #include <string>
 #include <utility>
 #include <vector>
 
@@ skipping 648 matching lines @@
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 // RenderViewHost, IPC message handlers:
 
 bool RenderViewHost::OnMessageReceived(const IPC::Message& msg) {
   if (!BrowserMessageFilter::CheckCanDispatchOnUI(msg, this))
     return true;
 
   // Filter out most IPC messages if this renderer is swapped out.
-  // We still want to certain ACKs to keep our state consistent.
-  if (is_swapped_out_)
-    if (!content::SwappedOutMessages::CanHandleWhileSwappedOut(msg))
+  // We still want to handle certain ACKs to keep our state consistent.
+  if (is_swapped_out_) {
+    if (!content::SwappedOutMessages::CanHandleWhileSwappedOut(msg)) {
+      // If this is a synchronous message and we decided not to handle it,
+      // we must send an error reply, or else the renderer will be stuck
+      // and won't respond to future requests.
+      if (msg.is_sync()) {
+        IPC::Message* reply = IPC::SyncMessage::GenerateReply(&msg);
+        reply->set_reply_error();
+        Send(reply);
+      }
+      // Don't continue looking for someone to handle it.
       return true;
+    }
+  }
 
   ObserverListBase<content::RenderViewHostObserver>::Iterator it(observers_);
   content::RenderViewHostObserver* observer;
   while ((observer = it.GetNext()) != NULL) {
     if (observer->OnMessageReceived(msg))
       return true;
   }
 
   if (delegate_->OnMessageReceived(msg))
     return true;
@@ skipping 851 matching lines @@
 
 void RenderViewHost::OnWebUISend(const GURL& source_url,
                                  const std::string& name,
                                  const base::ListValue& args) {
   delegate_->WebUISend(this, source_url, name, args);
 }
 
 void RenderViewHost::ClearPowerSaveBlockers() {
   STLDeleteValues(&power_save_blockers_);
 }