Remove limitation that renderer can't send sync IPCs to the UI thread in the browser.

content/public/browser/browser_message_filter.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/public/browser/browser_message_filter.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/command_line.h"
 #include "base/logging.h"
@@ skipping 51 matching lines @@
       if (runner.get()) {
         runner->PostTask(
             FROM_HERE,
             base::Bind(
                 base::IgnoreResult(&Internal::DispatchMessage), this, message));
         return true;
       }
       return DispatchMessage(message);
     }
 
-    if (thread == BrowserThread::UI &&
-        !BrowserMessageFilter::CheckCanDispatchOnUI(message, filter_.get())) {
-      return true;
-    }
-
     BrowserThread::PostTask(
         thread, FROM_HERE,
         base::Bind(
             base::IgnoreResult(&Internal::DispatchMessage), this, message));
     return true;
   }
 
   bool GetSupportedMessageClasses(
       std::vector<uint32_t>* supported_message_classes) const override {
     supported_message_classes->assign(
@@ skipping 63 matching lines @@
 
   delete message;
   return false;
 }
 
 base::TaskRunner* BrowserMessageFilter::OverrideTaskRunnerForMessage(
     const IPC::Message& message) {
   return nullptr;
 }
 
-bool BrowserMessageFilter::CheckCanDispatchOnUI(const IPC::Message& message,
-                                                IPC::Sender* sender) {
-#if defined(OS_WIN)
-  // On Windows there's a potential deadlock with sync messsages going in
-  // a circle from browser -> plugin -> renderer -> browser.
-  // On Linux we can avoid this by avoiding sync messages from browser->plugin.
-  // On Mac we avoid this by not supporting windowed plugins.
-  if (message.is_sync() && !message.is_caller_pumping_messages()) {
-    // NOTE: IF YOU HIT THIS ASSERT, THE SOLUTION IS ALMOST NEVER TO RUN A
-    // NESTED MESSAGE LOOP IN THE RENDERER!!!
-    // That introduces reentrancy which causes hard to track bugs.  You should
-    // find a way to either turn this into an asynchronous message, or one
-    // that can be answered on the IO thread.
-    NOTREACHED() << "Can't send sync messages to UI thread without pumping "
-        "messages in the renderer or else deadlocks can occur if the page "
-        "has windowed plugins! (message type " << message.type() << ")";
-    IPC::Message* reply = IPC::SyncMessage::GenerateReply(&message);
-    reply->set_reply_error();
-    sender->Send(reply);
-    return false;
-  }
-#endif
-  return true;
-}
-
 void BrowserMessageFilter::ShutdownForBadMessage() {
   base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
   if (command_line->HasSwitch(switches::kDisableKillAfterBadIPC))
     return;
 
   BrowserChildProcessHostImpl::HistogramBadMessageTerminated(
       PROCESS_TYPE_RENDERER);
 
 #if defined(OS_ANDROID)
   // Android requires a different approach for killing.
   StopChildProcess(peer_process_.Handle());
 #else
   peer_process_.Terminate(content::RESULT_CODE_KILLED_BAD_MESSAGE, false);
 #endif
 }
 
 BrowserMessageFilter::~BrowserMessageFilter() {
 }
 
 IPC::MessageFilter* BrowserMessageFilter::GetFilter() {
   // We create this on demand so that if a filter is used in a unit test but
   // never attached to a channel, we don't leak Internal and this;
   DCHECK(!internal_) << "Should only be called once.";
   internal_ = new Internal(this);
   return internal_;
 }
 
 }  // namespace content