Support for 'async' in the old formatter.

pkg/analyzer/lib/src/services/formatter_impl.dart

Index: pkg/analyzer/lib/src/services/formatter_impl.dart
diff --git a/pkg/analyzer/lib/src/services/formatter_impl.dart b/pkg/analyzer/lib/src/services/formatter_impl.dart
index 8cc329d6d553d49483834f2abbe3fa0d4575c340..dcfb34a2294787350d29441ad4d14a92728300bc 100644
--- a/pkg/analyzer/lib/src/services/formatter_impl.dart
+++ b/pkg/analyzer/lib/src/services/formatter_impl.dart
@@ -507,6 +507,7 @@ class SourceVisitor implements AstVisitor {
   }
 
   visitBlockFunctionBody(BlockFunctionBody node) {
+    token(node.keyword, followedBy: nonBreakingSpace);
     visit(node.block);
   }
 
@@ -782,6 +783,7 @@ class SourceVisitor implements AstVisitor {
 
   visitExpressionFunctionBody(ExpressionFunctionBody node) {
     int weight = lastSpaceWeight++;
+    token(node.keyword, followedBy: nonBreakingSpace);
     token(node.functionDefinition);
     levelSpace(weight);
     visit(node.expression);