LibWeb: Protect animation frame callbacks from GC while they execute

Stealing the callbacks from the AnimationFrameCallbackDriver made them
no longer safe from GC. Continue to store them on the class until we
have finished their execution.

Tests/LibWeb/Text/expected/HTML/requestAnimationFrame-gc.txt

@@ -0,0 +1,2 @@
+Collect garbage
+PASS! (Didn't crash)

Tests/LibWeb/Text/input/HTML/requestAnimationFrame-gc.html

@@ -0,0 +1,14 @@
+<script src="../include.js"></script>
+<script>
+    asyncTest((done) => {
+        requestAnimationFrame(() => {
+            println("Collect garbage");
+            internals.gc();
+        });
+
+        requestAnimationFrame(() => {
+            println("PASS! (Didn't crash)");
+            done();
+        });
+    });
+</script>

Userland/Libraries/LibWeb/HTML/AnimationFrameCallbackDriver.cpp

@@ -6,6 +6,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/ScopeGuard.h>
 #include <LibWeb/HTML/AnimationFrameCallbackDriver.h>
 
 namespace Web::HTML {
@@ -16,6 +17,7 @@ void AnimationFrameCallbackDriver::visit_edges(Cell::Visitor& visitor)
 {
     Base::visit_edges(visitor);
     visitor.visit(m_callbacks);
+    visitor.visit(m_executing_callbacks);
 }
 
 WebIDL::UnsignedLong AnimationFrameCallbackDriver::add(Callback handler)
@@ -37,8 +39,10 @@ bool AnimationFrameCallbackDriver::has_callbacks() const
 
 void AnimationFrameCallbackDriver::run(double now)
 {
-    auto taken_callbacks = move(m_callbacks);
-    for (auto& [id, callback] : taken_callbacks)
+    AK::ScopeGuard guard { [&]() { m_executing_callbacks.clear(); } };
+    m_executing_callbacks = move(m_callbacks);
+
+    for (auto& [id, callback] : m_executing_callbacks)
         callback->function()(now);
 }
 

Userland/Libraries/LibWeb/HTML/AnimationFrameCallbackDriver.h

@@ -34,6 +34,7 @@ private:
     WebIDL::UnsignedLong m_animation_frame_callback_identifier { 0 };
 
     OrderedHashMap<WebIDL::UnsignedLong, Callback> m_callbacks;
+    OrderedHashMap<WebIDL::UnsignedLong, Callback> m_executing_callbacks;
 };
 
 }