Fix hotReload for Flutter in clientside dartpad backend

R=goderbauer
Change-Id: Id704c270ba851b987d84b76c652eb8a1b7ceeafb
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/508102
Commit-Queue: Michael Goderbauer <goderbauer@google.com>
Reviewed-by: Michael Goderbauer <goderbauer@google.com>
Auto-Submit: Jonas Jensen <jonasfj@google.com>
Commit-Queue: Jonas Jensen <jonasfj@google.com>

pkg/dartpad/lib/dartpad.dart

@@ -19,7 +19,8 @@ import 'src/worker_client.dart';
 export 'src/dartpad_config.dart' show DartPadConfig;
 export 'src/exceptions.dart' hide rethrowAsDartPadException;
 export 'src/sandbox.dart' show Sandbox;
-export 'src/worker_client.dart' show LanguageServer, Workspace;
+export 'src/worker_client.dart'
+    show HotReloadCompiler, LanguageServer, Workspace;
 
 /// A client for interacting with a DartPad Web Worker.
 final class DartPad extends WorkerClient {

pkg/dartpad_worker/lib/src/asset/sandbox.js

@@ -321,6 +321,9 @@
 
     try {
       await self.dartDevEmbedder.hotReload(filesToLoad, librariesToReload);
+      if (self.dartDevEmbedder.debugger.extensionNames.includes('ext.flutter.reassemble')) {
+        await self.dartDevEmbedder.debugger.invokeExtension('ext.flutter.reassemble', '{}');
+      }
       return { generation: self.dartDevEmbedder.hotReloadGeneration };
     } catch (e) {
       throw new RpcError(e.message || String(e), errorCode.HOT_RELOAD_FAILED);