cef/patch/patches/message_loop.patch

diff --git base/message_loop/message_loop_current.cc base/message_loop/message_loop_current.cc
index 14d7b8fbb596..4cf58414c2f0 100644
--- base/message_loop/message_loop_current.cc
+++ base/message_loop/message_loop_current.cc
@@ -47,6 +47,8 @@ void MessageLoopCurrent::AddDestructionObserver(
 
 void MessageLoopCurrent::RemoveDestructionObserver(
     DestructionObserver* destruction_observer) {
+  if (!current_)
+    return;
   DCHECK(current_->IsBoundToCurrentThread());
   current_->RemoveDestructionObserver(destruction_observer);
 }
diff --git base/message_loop/message_loop_current.h base/message_loop/message_loop_current.h
index 462098e2522a..b853e6dc0c40 100644
--- base/message_loop/message_loop_current.h
+++ base/message_loop/message_loop_current.h
@@ -117,6 +117,12 @@ class BASE_EXPORT MessageLoopCurrent {
   // posted tasks.
   void SetAddQueueTimeToTasks(bool enable);
 
+#if defined(OS_WIN)
+  void set_os_modal_loop(bool os_modal_loop) { os_modal_loop_ = os_modal_loop; }
+
+  bool os_modal_loop() const { return os_modal_loop_; }
+#endif  // OS_WIN
+
   // Enables nested task processing in scope of an upcoming native message loop.
   // Some unwanted message loops may occur when using common controls or printer
   // functions. Hence, nested task processing is disabled by default to avoid
@@ -183,6 +189,13 @@ class BASE_EXPORT MessageLoopCurrent {
   friend class web::WebTaskEnvironment;
 
   sequence_manager::internal::SequenceManagerImpl* current_;
+
+#if defined(OS_WIN)
+ private:
+  // Should be set to true before calling Windows APIs like TrackPopupMenu, etc.
+  // which enter a modal message loop.
+  bool os_modal_loop_ = false;
+#endif
 };
 
 #if !defined(OS_NACL)
diff --git base/message_loop/message_pump_win.cc base/message_loop/message_pump_win.cc
index 4c500064bcd8..9b82c906b659 100644
--- base/message_loop/message_pump_win.cc
+++ base/message_loop/message_pump_win.cc
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include "base/message_loop/message_loop_current.h"
 #include "base/message_loop/message_pump_win.h"
 
 #include <algorithm>
@@ -497,7 +498,17 @@ bool MessagePumpForUI::ProcessNextWindowsMessage() {
     TRACE_EVENT1("base",
                  "MessagePumpForUI::ProcessNextWindowsMessage PeekMessage",
                  "sent_messages_in_queue", more_work_is_plausible);
-    has_msg = ::PeekMessage(&msg, nullptr, 0, 0, PM_REMOVE) != FALSE;
+
+    // We should not process all window messages if we are in the context of an
+    // OS modal loop, i.e. in the context of a windows API call like MessageBox.
+    // This is to ensure that these messages are peeked out by the OS modal loop.
+    if (MessageLoopCurrent::Get()->os_modal_loop()) {
+      // We only peek out WM_PAINT and WM_TIMER here for reasons mentioned above.
+      has_msg = PeekMessage(&msg, NULL, WM_PAINT, WM_PAINT, PM_REMOVE) ||
+                PeekMessage(&msg, NULL, WM_TIMER, WM_TIMER, PM_REMOVE);
+    } else {
+      has_msg = PeekMessage(&msg, NULL, 0, 0, PM_REMOVE) != FALSE;
+    }
   }
   if (has_msg)
     more_work_is_plausible |= ProcessMessageHelper(msg);