LibWeb: Clear all active timers when document is destroyed

This change implements a step from the document's destroy procedure in
the specification, saying that all active timers should be cleared.

By doing this, we also fix the leaking of a document in case where we
have navigated away from a page that has scheduled timers that haven't
yet been triggered.

Userland/Libraries/LibWeb/HTML/Timer.cpp

@@ -34,6 +34,7 @@ void Timer::visit_edges(Cell::Visitor& visitor)
 
 Timer::~Timer()
 {
+    VERIFY(!m_timer->is_active());
 }
 
 void Timer::start()
@@ -41,4 +42,9 @@ void Timer::start()
     m_timer->start();
 }
 
+void Timer::stop()
+{
+    m_timer->stop();
+}
+
 }

Userland/Libraries/LibWeb/HTML/Timer.h

@@ -24,6 +24,7 @@ public:
     virtual ~Timer() override;
 
     void start();
+    void stop();
 
 private:
     Timer(JS::Object& window, i32 milliseconds, Function<void()> callback, i32 id);

Userland/Libraries/LibWeb/HTML/WindowOrWorkerGlobalScope.cpp

@@ -183,15 +183,26 @@ i32 WindowOrWorkerGlobalScopeMixin::set_interval(TimerHandler handler, i32 timeo
 // https://html.spec.whatwg.org/multipage/timers-and-user-prompts.html#dom-cleartimeout
 void WindowOrWorkerGlobalScopeMixin::clear_timeout(i32 id)
 {
+    if (auto timer = m_timers.get(id); timer.has_value())
+        timer.value()->stop();
     m_timers.remove(id);
 }
 
 // https://html.spec.whatwg.org/multipage/timers-and-user-prompts.html#dom-clearinterval
 void WindowOrWorkerGlobalScopeMixin::clear_interval(i32 id)
 {
+    if (auto timer = m_timers.get(id); timer.has_value())
+        timer.value()->stop();
     m_timers.remove(id);
 }
 
+void WindowOrWorkerGlobalScopeMixin::clear_map_of_active_timers()
+{
+    for (auto& it : m_timers)
+        it.value->stop();
+    m_timers.clear();
+}
+
 // https://html.spec.whatwg.org/multipage/timers-and-user-prompts.html#timer-initialisation-steps
 // With no active script fix from https://github.com/whatwg/html/pull/9712
 i32 WindowOrWorkerGlobalScopeMixin::run_timer_initialization_steps(TimerHandler handler, i32 timeout, JS::MarkedVector<JS::Value> arguments, Repeat repeat, Optional<i32> previous_id)

Userland/Libraries/LibWeb/HTML/WindowOrWorkerGlobalScope.h

@@ -46,6 +46,7 @@ public:
     i32 set_interval(TimerHandler, i32 timeout, JS::MarkedVector<JS::Value> arguments);
     void clear_timeout(i32);
     void clear_interval(i32);
+    void clear_map_of_active_timers();
 
     PerformanceTimeline::PerformanceEntryTuple& relevant_performance_entry_tuple(FlyString const& entry_type);
     void queue_performance_entry(JS::NonnullGCPtr<PerformanceTimeline::PerformanceEntry> new_entry);