script: Don't panic when IPC WebRender APIs fail during shutdown.

components/script/dom/htmlmediaelement.rs

@@ -213,7 +213,10 @@ impl VideoFrameRenderer for MediaFrameRenderer {
             Some((ref mut image_key, ref mut width, ref mut height)) => {
                 self.old_frame = Some(*image_key);
 
-                let new_image_key = self.api.generate_image_key();
+                let new_image_key = match self.api.generate_image_key() {
+                    Ok(key) => key,
+                    Err(()) => return,
+                };
 
                 /* update current_frame */
                 *image_key = new_image_key;
@@ -243,7 +246,10 @@ impl VideoFrameRenderer for MediaFrameRenderer {
                 updates.push(ImageUpdate::AddImage(new_image_key, descriptor, image_data));
             },
             None => {
-                let image_key = self.api.generate_image_key();
+                let image_key = match self.api.generate_image_key() {
+                    Ok(key) => key,
+                    Err(()) => return,
+                };
                 self.current_frame = Some((image_key, frame.get_width(), frame.get_height()));
 
                 let image_data = if frame.is_gl_texture() && self.player_id.is_some() {

components/script_traits/lib.rs

@@ -1195,12 +1195,12 @@ impl WebrenderIpcSender {
     }
 
     /// Create a new image key. Blocks until the key is available.
-    pub fn generate_image_key(&self) -> ImageKey {
+    pub fn generate_image_key(&self) -> Result<ImageKey, ()> {
         let (sender, receiver) = ipc::channel().unwrap();
         self.0
             .send(WebrenderMsg::GenerateImageKey(sender))
-            .expect("error sending image key generation");
-        receiver.recv().expect("error receiving image key result")
+            .map_err(|_| ())?;
+        receiver.recv().map_err(|_| ())
     }
 
     /// Perform a resource update operation.