src/patch/patches/message_loop.patch

diff --git base/message_loop/message_loop_current.cc base/message_loop/message_loop_current.cc
index 7688ba3d7b0d..9acaaa0d5c7f 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 61b8c6fcc42d..d439b00a87bb 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 or disables the recursive task processing. This happens in the case
   // of recursive message loops. Some unwanted message loops may occur when
   // using common controls or printer functions. By default, recursive task
@@ -186,6 +192,13 @@ 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 c50e34f6da1b..40dcc66ed82a 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>
@@ -493,10 +494,18 @@ bool MessagePumpForUI::ProcessPumpReplacementMessage() {
   // asynchronous to this thread!!
 
   MSG msg;
-  const bool have_message =
-      ::PeekMessage(&msg, nullptr, 0, 0, PM_REMOVE) != FALSE;
+  bool have_message = 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.
+    have_message = PeekMessage(&msg, NULL, WM_PAINT, WM_PAINT, PM_REMOVE) ||
+                   PeekMessage(&msg, NULL, WM_TIMER, WM_TIMER, PM_REMOVE);
+  } else {
+    have_message = PeekMessage(&msg, NULL, 0, 0, PM_REMOVE) != FALSE;
+  }
 
-  // Expect no message or a message different than kMsgHaveWork.
   DCHECK(!have_message || kMsgHaveWork != msg.message ||
          msg.hwnd != message_window_.hwnd());