Fix bot failure because of missed update of AssertStatement

pkg/analyzer/lib/src/kernel/ast_from_analyzer.dart

Index: pkg/analyzer/lib/src/kernel/ast_from_analyzer.dart
diff --git a/pkg/analyzer/lib/src/kernel/ast_from_analyzer.dart b/pkg/analyzer/lib/src/kernel/ast_from_analyzer.dart
index 9a26298d911b3e550774a292bbde0ead98e49658..492bb6fc0fde62ac2457972fd51e5c56259d155c 100644
--- a/pkg/analyzer/lib/src/kernel/ast_from_analyzer.dart
+++ b/pkg/analyzer/lib/src/kernel/ast_from_analyzer.dart
@@ -999,7 +999,7 @@ class StatementBuilder extends GeneralizingAstVisitor<ast.Statement> {
 
   ast.Statement visitAssertStatement(AssertStatement node) {
     return new ast.AssertStatement(scope.buildExpression(node.condition),
-        scope.buildOptionalExpression(node.message));
+        message: scope.buildOptionalExpression(node.message));
   }
 
   ast.Statement visitBlock(Block node) {