Reland: Increase threshold for usage of compute for utf8 decoding on large...

Reland: Increase threshold for usage of compute for utf8 decoding on large strings to 50 KB (#64498)

packages/flutter/lib/src/services/asset_bundle.dart

@@ -71,11 +71,13 @@ abstract class AssetBundle {
     // that the null-handling logic is dead code).
     if (data == null)
       throw FlutterError('Unable to load asset: $key'); // ignore: dead_code
-    if (data.lengthInBytes < 10 * 1024) {
-      // 10KB takes about 3ms to parse on a Pixel 2 XL.
-      // See: https://github.com/dart-lang/sdk/issues/31954
+    // 50 KB of data should take 2-3 ms to parse on a Moto G4, and about 400 μs
+    // on a Pixel 4.
+    if (data.lengthInBytes < 50 * 1024) {
       return utf8.decode(data.buffer.asUint8List());
     }
+    // For strings larger than 50 KB, run the computation in an isolate to
+    // avoid causing main thread jank.
     return compute(_utf8decode, data, debugLabel: 'UTF8 decode for "$key"');
   }
 

packages/flutter_tools/lib/src/run_hot.dart

@@ -562,9 +562,11 @@ class HotRunner extends ResidentRunner {
         } on vm_service.RPCError {
           // Do nothing, we're already subcribed.
         }
+        // Ideally this would wait for kIsolateRunnable, but either this subscription occurs too
+        // late to receive the event, or it is not forwarded for hot restarted isolates.
         isolateNotifications.add(
           device.vmService.onIsolateEvent.firstWhere((vm_service.Event event) {
-            return event.kind == vm_service.EventKind.kIsolateRunnable;
+            return event.kind == vm_service.EventKind.kServiceExtensionAdded;
           }),
         );
       }