obs-browser: flush panel cookie store on exit

If cookie store is not flushed, state might become inconsistent:
reading from the cookies file will become impossible.
No errors will be returned, yet no information will be available,
and no information will be stored: the cookie manager will appear to be
empty at all times and the `Cookies` file modified date will not update
moving forward.

This will result, for example, in Twitch chat window re-opening for
users which connected their Twitch account, but not having the
`auth-token` cookie available: once the user will try to send a
message to the chat, they will be redirected to Twitch login screen.

obs-browser-plugin.cpp

@@ -77,6 +77,72 @@ bool QueueCEFTask(std::function<void()> task)
 
 /* ========================================================================= */
 
+static std::mutex cookie_managers_mutex;
+static std::vector<CefRefPtr<CefCookieManager>> cookie_managers;
+
+void register_cookie_manager(CefRefPtr<CefCookieManager> cm)
+{
+	std::lock_guard<std::mutex> guard(cookie_managers_mutex);
+
+	cookie_managers.emplace_back(cm);
+}
+
+static void flush_cookie_manager(CefRefPtr<CefCookieManager> cm)
+{
+	os_event_t* complete_event;
+
+	os_event_init(&complete_event, OS_EVENT_TYPE_AUTO);
+
+	class CompletionCallback : public CefCompletionCallback
+	{
+	public:
+		CompletionCallback(os_event_t* complete_event) : m_complete_event(complete_event)
+		{
+		}
+
+		virtual void OnComplete() override
+		{
+			os_event_signal(m_complete_event);
+		}
+
+		IMPLEMENT_REFCOUNTING(CompletionCallback);
+
+	private:
+		os_event_t* m_complete_event;
+	};
+
+	CefRefPtr<CefCompletionCallback> callback =
+		new CompletionCallback(complete_event);
+
+	auto task = [&]() {
+		if (!cm->FlushStore(callback)) {
+			blog(LOG_WARNING,
+				"Failed flushing cookie store");
+
+			os_event_signal(complete_event);
+		}
+		else {
+			blog(LOG_INFO, "Flushed cookie store");
+		}
+	};
+
+	CefPostTask(TID_IO, CefRefPtr<BrowserTask>(new BrowserTask(task)));
+
+	os_event_wait(complete_event);
+	os_event_destroy(complete_event);
+}
+
+static void flush_cookie_managers()
+{
+	std::lock_guard<std::mutex> guard(cookie_managers_mutex);
+
+	for (auto cm : cookie_managers) {
+		flush_cookie_manager(cm);
+	}
+}
+
+/* ========================================================================= */
+
 static const char *default_css = "\
 body { \
 background-color: rgba(0, 0, 0, 0); \
@@ -500,6 +566,8 @@ bool obs_module_load(void)
 
 void obs_module_unload(void)
 {
+	flush_cookie_managers();
+
 	if (manager_thread.joinable()) {
 		while (!QueueCEFTask([] () {CefQuitMessageLoop();}))
 			os_sleep_ms(5);

panel/browser-panel.cpp

@@ -13,6 +13,8 @@ extern bool QueueCEFTask(std::function<void()> task);
 extern "C" void obs_browser_initialize(void);
 extern os_event_t *cef_started_event;
 
+void register_cookie_manager(CefRefPtr<CefCookieManager> cm);
+
 std::mutex                      popup_whitelist_mutex;
 std::vector<PopupWhitelistInfo> popup_whitelist;
 std::vector<PopupWhitelistInfo> forced_popups;
@@ -83,6 +85,8 @@ struct QCefCookieManagerInternal : QCefCookieManager {
 		if (!cm)
 			throw "Failed to create cookie manager";
 
+		register_cookie_manager(cm);
+
 		rch = new QCefRequestContextHandler(cm);
 
 		rc = CefRequestContext::CreateContext(