macOS/iOS: Fix auto trait impls of EventLoopProxy (#1084)

* macOS/iOS: Fix auto trait impls of `EventLoopProxy`

`EventLoopProxy<T>` allows sending `T` from an arbitrary thread that
owns the proxy object. Thus, if `T` is `!Send`, `EventLoopProxy<T>` must
not be allowed to leave the main thread.

`EventLoopProxy<T>` uses `std::sync::mpsc::Sender` under the hood,
meaning the `!Sync` restriction of it also applies to
`EventLoopProxy<T>`. That is, even if `T` is thread-safe, a single
`EventLoopProxy` object cannot be shared between threads.

* Update `CHANGELOG.md`

CHANGELOG.md

@@ -21,7 +21,8 @@
 - On Linux, the functions `is_wayland`, `is_x11`, `xlib_xconnection` and `wayland_display` have been moved to a new `EventLoopWindowTargetExtUnix` trait.
 - On iOS, add `set_prefers_status_bar_hidden` extension function instead of
   hijacking `set_decorations` for this purpose.
-  
+- On macOS and iOS, corrected the auto trait impls of `EventLoopProxy`.
+
 # 0.20.0 Alpha 2 (2019-07-09)
 
 - On X11, non-resizable windows now have maximize explicitly disabled.

src/platform_impl/ios/event_loop.rs

@@ -142,8 +142,7 @@ pub struct EventLoopProxy<T> {
     source: CFRunLoopSourceRef,
 }
 
-unsafe impl<T> Send for EventLoopProxy<T> {}
+unsafe impl<T: Send> Send for EventLoopProxy<T> {}
-unsafe impl<T> Sync for EventLoopProxy<T> {}
 
 impl<T> Clone for EventLoopProxy<T> {
     fn clone(&self) -> EventLoopProxy<T> {

src/platform_impl/macos/event_loop.rs

@@ -113,8 +113,7 @@ pub struct Proxy<T> {
     source: CFRunLoopSourceRef,
 }
 
-unsafe impl<T> Send for Proxy<T> {}
+unsafe impl<T: Send> Send for Proxy<T> {}
-unsafe impl<T> Sync for Proxy<T> {}
 
 impl<T> Clone for Proxy<T> {
     fn clone(&self) -> Self {