Fix parsing [a]sync[*] function body modifiers with Fasta.

pkg/front_end/lib/src/fasta/parser/parser.dart

Index: pkg/front_end/lib/src/fasta/parser/parser.dart
diff --git a/pkg/front_end/lib/src/fasta/parser/parser.dart b/pkg/front_end/lib/src/fasta/parser/parser.dart
index 61d741736f90a986b8357baf92a8c2f4c87753c3..d7ed9c1a84c177005158c79692e098b079679eb4 100644
--- a/pkg/front_end/lib/src/fasta/parser/parser.dart
+++ b/pkg/front_end/lib/src/fasta/parser/parser.dart
@@ -2009,9 +2009,9 @@ class Parser {
       token = parseExpression(token.next);
       if (!isExpression) {
         expectSemicolon(token);
-        listener.endReturnStatement(true, begin, token);
+        listener.endExpressionFunctionBody(begin, token);
       } else {
-        listener.endReturnStatement(true, begin, null);
+        listener.endExpressionFunctionBody(begin, null);
       }
       return token;
     } else if (optional('=', token)) {
@@ -2021,9 +2021,9 @@ class Parser {
       token = parseExpression(token.next);
       if (!isExpression) {
         expectSemicolon(token);
-        listener.endReturnStatement(true, begin, token);
+        listener.endExpressionFunctionBody(begin, token);
       } else {
-        listener.endReturnStatement(true, begin, null);
+        listener.endExpressionFunctionBody(begin, null);
       }
       return token;
     }