Stop using nested message loop for alert() and other JS dialogs

content/renderer/render_thread_impl.cc

Index: content/renderer/render_thread_impl.cc
diff --git a/content/renderer/render_thread_impl.cc b/content/renderer/render_thread_impl.cc
index c81e108be2fee15ac2e233e91f3a4035618ed098..4582ad8d8ad84960f1d75c8e14826aec8091c579 100644
--- a/content/renderer/render_thread_impl.cc
+++ b/content/renderer/render_thread_impl.cc
@@ -614,7 +614,6 @@ void RenderThreadImpl::Init(
   InitializeWebKit(resource_task_queue);
 
   // In single process the single process is all there is.
-  notify_webkit_of_modal_loop_ = true;
   webkit_shared_timer_suspended_ = false;
   widget_count_ = 0;
   hidden_widget_count_ = 0;
@@ -959,22 +958,15 @@ bool RenderThreadImpl::Send(IPC::Message* msg) {
     }
   }
 
-  bool notify_webkit_of_modal_loop = true;  // default value
-  std::swap(notify_webkit_of_modal_loop, notify_webkit_of_modal_loop_);
-
   if (pumping_events) {
     renderer_scheduler_->SuspendTimerQueue();
-
-    if (notify_webkit_of_modal_loop)
-      WebView::willEnterModalLoop();
+    WebView::willEnterModalLoop();

[no sievers, 2016/05/18 20:11:24]

...and related to that: why do we still need to tell webkit if we won't dispatch
nested messages anymore?

[Changwan Ryu, 2016/05/19 00:44:56]

PrintWebViewHelper and FlashMessageLoop may need to pause resource dispatching
until their sync messages get replies. JS dialogues were exceptions where we did
not have to notify webkit.

[Lei Zhang, 2016/05/19 00:50:28]

window.print() is still a thing and it is synchronous.

[Changwan Ryu, 2016/05/19 01:00:31]

Thanks for the correction. I mean alert(), beforeunload(), confirm(), and
prompt(). window.print() goes through PrintWebViewHelper and still pumps
messages.

   }
 
   bool rv = ChildThreadImpl::Send(msg);
 
   if (pumping_events) {
-    if (notify_webkit_of_modal_loop)
-      WebView::didExitModalLoop();
-
+    WebView::didExitModalLoop();
     renderer_scheduler_->ResumeTimerQueue();
   }
 
@@ -1620,10 +1612,6 @@ std::unique_ptr<base::SharedMemory> RenderThreadImpl::AllocateSharedMemory(
   return HostAllocateSharedMemoryBuffer(size);
 }
 
-void RenderThreadImpl::DoNotNotifyWebKitOfModalLoop() {
-  notify_webkit_of_modal_loop_ = false;
-}
-
 void RenderThreadImpl::OnChannelError() {
   // In single-process mode, the renderer can't be restarted after shutdown.
   // So, if we get a channel error, crash the whole process right now to get a