On Web, implement Send and Sync where appropriate (#2834)

src/platform_impl/web/event_loop/proxy.rs

@@ -1,18 +1,24 @@
 use super::runner;
 use crate::event::Event;
 use crate::event_loop::EventLoopClosed;
+use crate::platform_impl::platform::r#async::Channel;
 
 pub struct EventLoopProxy<T: 'static> {
-    runner: runner::Shared<T>,
+    runner: Channel<runner::Shared<T>, T>,
 }
 
 impl<T: 'static> EventLoopProxy<T> {
     pub fn new(runner: runner::Shared<T>) -> Self {
-        Self { runner }
+        Self {
+            runner: Channel::new(runner, |runner, event| {
+                runner.send_event(Event::UserEvent(event))
+            })
+            .unwrap(),
+        }
     }
 
     pub fn send_event(&self, event: T) -> Result<(), EventLoopClosed<T>> {
-        self.runner.send_event(Event::UserEvent(event));
+        self.runner.send(event);
         Ok(())
     }
 }