LibWeb: Basic implementation of global event handlers :^)

Document and HTMLElement now inherit from HTML::GlobalEventHandlers
which allows them to support "onfoo" event handler attributes.

These are assignable both via IDL attributes and content attributes.

Event listeners constructed this way get a special "attribute" flag
on them so we know which one to replace if you reassign them.
This also allows them to coexist with EventTarget.addEventListener().

This is all a bit sloppy, but it works decently for a first cut.
The Window object should also inherit GlobalEventHandlers, but since
we don't generate it from IDL, I haven't taken that step here.

Also this would be a lot nicer if we supported IDL mixins.

Userland/Libraries/LibWeb/DOM/Document.h

@@ -55,6 +55,7 @@ enum class QuirksMode {
 class Document
     : public ParentNode
     , public NonElementParentNode<Document>
+    , public HTML::GlobalEventHandlers
     , public Bindings::ScriptExecutionContext {
 public:
     using WrapperType = Bindings::DocumentWrapper;
@@ -233,8 +234,12 @@ public:
 private:
     explicit Document(const URL&);
 
+    // ^DOM::Node
     virtual RefPtr<Layout::Node> create_layout_node() override;
 
+    // ^HTML::GlobalEventHandlers
+    virtual EventTarget& global_event_handlers_to_event_target() final { return *this; }
+
     void tear_down_layout_tree();
 
     void increment_referencing_node_count()

Userland/Libraries/LibWeb/DOM/Document.idl

@@ -36,4 +36,75 @@ interface Document : Node {
 
     attribute DOMString title;
 
+    // FIXME: These should all come from a GlobalEventHandlers mixin
+    attribute EventHandler onabort;
+    attribute EventHandler onauxclick;
+    attribute EventHandler onblur;
+    attribute EventHandler oncancel;
+    attribute EventHandler oncanplay;
+    attribute EventHandler oncanplaythrough;
+    attribute EventHandler onchange;
+    attribute EventHandler onclick;
+    attribute EventHandler onclose;
+    attribute EventHandler oncontextmenu;
+    attribute EventHandler oncuechange;
+    attribute EventHandler ondblclick;
+    attribute EventHandler ondrag;
+    attribute EventHandler ondragend;
+    attribute EventHandler ondragenter;
+    attribute EventHandler ondragleave;
+    attribute EventHandler ondragover;
+    attribute EventHandler ondragstart;
+    attribute EventHandler ondrop;
+    attribute EventHandler ondurationchange;
+    attribute EventHandler onemptied;
+    attribute EventHandler onended;
+
+    // FIXME: Should be an OnErrorEventHandler
+    attribute EventHandler onerror;
+
+    attribute EventHandler onfocus;
+    attribute EventHandler onformdata;
+    attribute EventHandler oninput;
+    attribute EventHandler oninvalid;
+    attribute EventHandler onkeydown;
+    attribute EventHandler onkeypress;
+    attribute EventHandler onkeyup;
+    attribute EventHandler onload;
+    attribute EventHandler onloadeddata;
+    attribute EventHandler onloadedmetadata;
+    attribute EventHandler onloadstart;
+    attribute EventHandler onmousedown;
+    [LegacyLenientThis] attribute EventHandler onmouseenter;
+    [LegacyLenientThis] attribute EventHandler onmouseleave;
+    attribute EventHandler onmousemove;
+    attribute EventHandler onmouseout;
+    attribute EventHandler onmouseover;
+    attribute EventHandler onmouseup;
+    attribute EventHandler onpause;
+    attribute EventHandler onplay;
+    attribute EventHandler onplaying;
+    attribute EventHandler onprogress;
+    attribute EventHandler onratechange;
+    attribute EventHandler onreset;
+    attribute EventHandler onresize;
+    attribute EventHandler onscroll;
+    attribute EventHandler onsecuritypolicyviolation;
+    attribute EventHandler onseeked;
+    attribute EventHandler onseeking;
+    attribute EventHandler onselect;
+    attribute EventHandler onslotchange;
+    attribute EventHandler onstalled;
+    attribute EventHandler onsubmit;
+    attribute EventHandler onsuspend;
+    attribute EventHandler ontimeupdate;
+    attribute EventHandler ontoggle;
+    attribute EventHandler onvolumechange;
+    attribute EventHandler onwaiting;
+    attribute EventHandler onwebkitanimationend;
+    attribute EventHandler onwebkitanimationiteration;
+    attribute EventHandler onwebkitanimationstart;
+    attribute EventHandler onwebkittransitionend;
+    attribute EventHandler onwheel;
+
 };

Userland/Libraries/LibWeb/DOM/EventListener.h

@@ -38,8 +38,9 @@ class EventListener
 public:
     using WrapperType = Bindings::EventListenerWrapper;
 
-    explicit EventListener(JS::Handle<JS::Function> function)
+    explicit EventListener(JS::Handle<JS::Function> function, bool is_attribute = false)
         : m_function(move(function))
+        , m_attribute(is_attribute)
     {
     }
 
@@ -60,6 +61,8 @@ public:
     bool removed() const { return m_removed; }
     void set_removed(bool removed) { m_removed = removed; }
 
+    bool is_attribute() const { return m_attribute; }
+
 private:
     FlyString m_type;
     JS::Handle<JS::Function> m_function;
@@ -67,6 +70,7 @@ private:
     bool m_passive { false };
     bool m_once { false };
     bool m_removed { false };
+    bool m_attribute { false };
 };
 
 }

Userland/Libraries/LibWeb/DOM/EventTarget.h

@@ -61,6 +61,7 @@ public:
         NonnullRefPtr<EventListener> listener;
     };
 
+    Vector<EventListenerRegistration>& listeners() { return m_listeners; }
     const Vector<EventListenerRegistration>& listeners() const { return m_listeners; }
 
     Function<void(const Event&)> activation_behaviour;