Core: Add a HookableEvent for UICommon::FlushUnsavedData.

Source/Core/UICommon/UICommon.cpp

@@ -65,6 +65,7 @@
 namespace UICommon
 {
 static Config::ConfigChangedCallbackID s_config_changed_callback_id;
+static Common::HookableEvent<> s_flush_unsaved_data_event_hook;
 
 static void CreateDumpPath(std::string path)
 {
@@ -162,9 +163,15 @@ void Shutdown()
   Config::Shutdown();
 }
 
+[[nodiscard]] Common::EventHook AddFlushUnsavedDataCallback(std::function<void()> callback)
+{
+  return s_flush_unsaved_data_event_hook.Register(std::move(callback));
+}
+
 void FlushUnsavedData()
 {
   INFO_LOG_FMT(CORE, "Flushing unsaved data...");
+  s_flush_unsaved_data_event_hook.Trigger();
 }
 
 void InitControllers(const WindowSystemInfo& wsi)

Source/Core/UICommon/UICommon.h

@@ -6,6 +6,7 @@
 #include <string>
 
 #include "Common/CommonTypes.h"
+#include "Common/HookableEvent.h"
 
 struct WindowSystemInfo;
 
@@ -14,6 +15,8 @@ namespace UICommon
 void Init();
 void Shutdown();
 
+// Triggered from the Host-thread on Android before a potential process termination.
+[[nodiscard]] Common::EventHook AddFlushUnsavedDataCallback(std::function<void()> callback);
 void FlushUnsavedData();
 
 void InitControllers(const WindowSystemInfo& wsi);