Revert 79470 - Ensure that BrowserMessageFilter isn't used to process a sync message on the UI th...

content/browser/renderer_host/render_view_host.cc

Index: content/browser/renderer_host/render_view_host.cc
===================================================================
--- content/browser/renderer_host/render_view_host.cc	(revision 79485)
+++ content/browser/renderer_host/render_view_host.cc	(working copy)
@@ -31,7 +31,6 @@
 #include "chrome/common/translate_errors.h"
 #include "chrome/common/url_constants.h"
 #include "chrome/common/web_apps.h"
-#include "content/browser/browser_message_filter.h"
 #include "content/browser/child_process_security_policy.h"
 #include "content/browser/cross_site_request_manager.h"
 #include "content/browser/in_process_webkit/session_storage_namespace.h"
@@ -700,8 +699,26 @@
 // RenderViewHost, IPC message handlers:
 
 bool RenderViewHost::OnMessageReceived(const IPC::Message& msg) {
-  if (!BrowserMessageFilter::CheckCanDispatchOnUI(msg, this))
+#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 (msg.is_sync() && !msg.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 " << msg.type() << ")";
+    IPC::Message* reply = IPC::SyncMessage::GenerateReply(&msg);
+    reply->set_reply_error();
+    Send(reply);
     return true;
+  }
+#endif
 
   if (delegate_->OnMessageReceived(msg))
     return true;