[core] Properly recycle Device::temp_suspected.

Change `Device::untrack` to properly reuse the `ResourceMap` allocated
for prior calls. The prior code tries to do this but always leaves
`Device::temp_suspected` set to a new empty `ResourceMap`, leaving the
previous value to be dropped by `ResourceMap::extend`.

Change `ResourceMap::extend` to take `other` by reference, rather than
taking it by value and dropping it.

wgpu-core/src/device/life.rs

@@ -93,7 +93,7 @@ impl<A: HalApi> ResourceMaps<A> {
         destroyed_textures.clear();
     }
 
-    pub(crate) fn extend(&mut self, mut other: Self) {
+    pub(crate) fn extend(&mut self, other: &mut Self) {
         let ResourceMaps {
             buffers,
             staging_buffers,

wgpu-core/src/device/resource.rs

@@ -485,12 +485,14 @@ impl<A: HalApi> Device<A> {
     }
 
     pub(crate) fn untrack(&self, trackers: &Tracker<A>) {
+        // If we have a previously allocated `ResourceMap`, just use that.
         let mut temp_suspected = self
             .temp_suspected
             .lock()
-            .replace(ResourceMaps::new())
-            .unwrap();
+            .take()
+            .unwrap_or_else(|| ResourceMaps::new());
         temp_suspected.clear();
+
         // As the tracker is cleared/dropped, we need to consider all the resources
         // that it references for destruction in the next GC pass.
         {
@@ -551,7 +553,11 @@ impl<A: HalApi> Device<A> {
                 }
             }
         }
-        self.lock_life().suspected_resources.extend(temp_suspected);
+        self.lock_life()
+            .suspected_resources
+            .extend(&mut temp_suspected);
+        // Save this resource map for later reuse.
+        *self.temp_suspected.lock() = Some(temp_suspected);
     }
 
     pub(crate) fn create_buffer(