Desktop: Add support for UI scaling (#3310)

* desktop support ui scaling

* fix some warnings

* use browser zoom if needed

* fix infinite footprint size

* fix web canvas scale

* always set zoom

* use only zoom for scaling

* prevent user zoom

* remove mouse position scaling

desktop/src/cef/internal/browser_process_load_handler.rs

@@ -0,0 +1,60 @@
+use cef::rc::{Rc, RcImpl};
+use cef::sys::{_cef_load_handler_t, cef_base_ref_counted_t, cef_load_handler_t};
+use cef::{ImplBrowser, ImplBrowserHost, ImplLoadHandler, WrapLoadHandler};
+
+use crate::cef::CefEventHandler;
+
+pub(crate) struct LoadHandlerImpl<H: CefEventHandler> {
+	object: *mut RcImpl<cef_load_handler_t, Self>,
+	event_handler: H,
+}
+impl<H: CefEventHandler> LoadHandlerImpl<H> {
+	pub(crate) fn new(event_handler: H) -> Self {
+		Self {
+			object: std::ptr::null_mut(),
+			event_handler,
+		}
+	}
+}
+
+impl<H: CefEventHandler> ImplLoadHandler for LoadHandlerImpl<H> {
+	fn on_loading_state_change(&self, browser: Option<&mut cef::Browser>, is_loading: ::std::os::raw::c_int, _can_go_back: ::std::os::raw::c_int, _can_go_forward: ::std::os::raw::c_int) {
+		let view_info = self.event_handler.view_info();
+
+		if let Some(browser) = browser
+			&& is_loading == 0
+		{
+			browser.host().unwrap().set_zoom_level(view_info.zoom());
+		}
+	}
+
+	fn get_raw(&self) -> *mut _cef_load_handler_t {
+		self.object.cast()
+	}
+}
+
+impl<H: CefEventHandler> Clone for LoadHandlerImpl<H> {
+	fn clone(&self) -> Self {
+		unsafe {
+			let rc_impl = &mut *self.object;
+			rc_impl.interface.add_ref();
+		}
+		Self {
+			object: self.object,
+			event_handler: self.event_handler.duplicate(),
+		}
+	}
+}
+impl<H: CefEventHandler> Rc for LoadHandlerImpl<H> {
+	fn as_base(&self) -> &cef_base_ref_counted_t {
+		unsafe {
+			let base = &*self.object;
+			std::mem::transmute(&base.cef_object)
+		}
+	}
+}
+impl<H: CefEventHandler> WrapLoadHandler for LoadHandlerImpl<H> {
+	fn wrap_rc(&mut self, object: *mut RcImpl<_cef_load_handler_t, Self>) {
+		self.object = object;
+	}
+}