dom: Add missing event handlers

Adding:
* global event handlers,
* window event handlers,
* document and element handlers,
* and support for BeforeUnloadEvent.

Signed-off-by: Piotr Stankiewicz <bionicrift@gmail.com>

components/script/dom/beforeunloadevent.rs

@@ -0,0 +1,67 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use dom::bindings::cell::DOMRefCell;
+use dom::bindings::codegen::Bindings::BeforeUnloadEventBinding;
+use dom::bindings::codegen::Bindings::BeforeUnloadEventBinding::BeforeUnloadEventMethods;
+use dom::bindings::codegen::Bindings::EventBinding::EventMethods;
+use dom::bindings::global::GlobalRef;
+use dom::bindings::inheritance::Castable;
+use dom::bindings::js::Root;
+use dom::bindings::reflector::reflect_dom_object;
+use dom::event::{Event, EventBubbles, EventCancelable};
+use string_cache::Atom;
+use util::str::DOMString;
+
+// https://html.spec.whatwg.org/multipage/#beforeunloadevent
+#[dom_struct]
+pub struct BeforeUnloadEvent {
+    event: Event,
+    return_value: DOMRefCell<DOMString>,
+}
+
+impl BeforeUnloadEvent {
+    fn new_inherited() -> BeforeUnloadEvent {
+        BeforeUnloadEvent {
+            event: Event::new_inherited(),
+            return_value: DOMRefCell::new(DOMString::new()),
+        }
+    }
+
+    pub fn new_uninitialized(global: GlobalRef) -> Root<BeforeUnloadEvent> {
+        reflect_dom_object(box BeforeUnloadEvent::new_inherited(),
+                           global,
+                           BeforeUnloadEventBinding::Wrap)
+    }
+
+    pub fn new(global: GlobalRef,
+               type_: Atom,
+               bubbles: EventBubbles,
+               cancelable: EventCancelable) -> Root<BeforeUnloadEvent> {
+        let ev = BeforeUnloadEvent::new_uninitialized(global);
+        {
+            let event = ev.upcast::<Event>();
+            event.init_event(type_, bool::from(bubbles),
+                             bool::from(cancelable));
+        }
+        ev
+    }
+}
+
+impl BeforeUnloadEventMethods for BeforeUnloadEvent {
+    // https://html.spec.whatwg.org/multipage/#dom-beforeunloadevent-returnvalue
+    fn ReturnValue(&self) -> DOMString {
+        self.return_value.borrow().clone()
+    }
+
+    // https://html.spec.whatwg.org/multipage/#dom-beforeunloadevent-returnvalue
+    fn SetReturnValue(&self, value: DOMString) {
+        *self.return_value.borrow_mut() = value;
+    }
+
+    // https://dom.spec.whatwg.org/#dom-event-istrusted
+    fn IsTrusted(&self) -> bool {
+        self.event.IsTrusted()
+    }
+}