Add assertions for clocks monotonicity (#9514)

Fixes #3491

Author: michalfita

internal/core/animations.rs

@@ -249,7 +249,9 @@ impl AnimationDriver {
     /// Iterates through all animations based on the new time tick and updates their state. This should be called by
     /// the windowing system driver for every frame.
     pub fn update_animations(&self, new_tick: Instant) {
-        if self.global_instant.as_ref().get_untracked() != new_tick {
+        let current_tick = self.global_instant.as_ref().get_untracked();
+        assert!(current_tick <= new_tick, "The platform's clock is not monotonic!");
+        if current_tick != new_tick {
             self.active_animations.set(false);
             self.global_instant.as_ref().set(new_tick);
         }

internal/core/platform.rs

@@ -94,7 +94,9 @@ pub trait Platform {
         #[cfg(feature = "std")]
         {
             let the_beginning = *INITIAL_INSTANT.get_or_init(time::Instant::now);
-            time::Instant::now() - the_beginning
+            let now = time::Instant::now();
+            assert!(now >= the_beginning, "The platform's clock is not monotonic!");
+            now - the_beginning
         }
         #[cfg(not(feature = "std"))]
         unimplemented!("The platform abstraction must implement `duration_since_start`")