Ensure user-thrown errors have ErrorSummary nodes (#36857)

packages/flutter/lib/src/foundation/assertions.dart

@@ -411,7 +411,7 @@ class FlutterErrorDetails extends Diagnosticable {
         String message = exceptionAsString();
         if (message.startsWith(prefix))
           message = message.substring(prefix.length);
-        properties.add(ErrorDescription('$message'));
+        properties.add(ErrorSummary('$message'));
       }
     }
 

packages/flutter/test/foundation/assertions_test.dart

@@ -328,4 +328,28 @@ void main() {
       );
     }
   });
+
+  test('User-thrown exceptions have ErrorSummary properties', () {
+    {
+      DiagnosticsNode node;
+      try {
+        throw 'User thrown string';
+      } catch (e) {
+        node = FlutterErrorDetails(exception: e).toDiagnosticsNode();
+      }
+      final ErrorSummary summary = node.getProperties().whereType<ErrorSummary>().single;
+      expect(summary.value, equals(<String>['User thrown string']));
+    }
+
+    {
+      DiagnosticsNode node;
+      try {
+        throw ArgumentError.notNull('myArgument');
+      } catch (e) {
+        node = FlutterErrorDetails(exception: e).toDiagnosticsNode();
+      }
+      final ErrorSummary summary = node.getProperties().whereType<ErrorSummary>().single;
+      expect(summary.value, equals(<String>['Invalid argument(s) (myArgument): Must not be null']));
+    }
+  });
 }