[dart2js] handle synthesized parameters in dump-info

Fixes https://github.com/dart-lang/sdk/issues/41459

Change-Id: I70fbe7ebcc79a948d23846cdb756cde77e9db230
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/143720
Reviewed-by: Mayank Patke <fishythefish@google.com>
Commit-Queue: Sigmund Cherem <sigmund@google.com>

pkg/compiler/lib/src/dump_info.dart

@@ -276,8 +276,10 @@ class ElementInfoCollector {
     });
     int parameterIndex = 0;
     closedWorld.elementEnvironment.forEachParameter(function, (type, name, _) {
-      parameters.add(new ParameterInfo(
-          name, inferredParameterTypes[parameterIndex++], '$type'));
+      // Synthesized parameters have no name. This can happen on parameters of
+      // setters derived from lowering late fields.
+      parameters.add(new ParameterInfo(name ?? '#t${parameterIndex}',
+          inferredParameterTypes[parameterIndex++], '$type'));
     });
 
     var functionType = environment.getFunctionType(function);