Restore invariant that stack is empty in parseFunctionBody.

pkg/front_end/lib/src/fasta/source/diet_listener.dart

Index: pkg/front_end/lib/src/fasta/source/diet_listener.dart
diff --git a/pkg/front_end/lib/src/fasta/source/diet_listener.dart b/pkg/front_end/lib/src/fasta/source/diet_listener.dart
index ab460fb3c76dd2472d150b57363e1c4281c6b40a..0691f739a47022b8d834604b44d70fea91a4f5c0 100644
--- a/pkg/front_end/lib/src/fasta/source/diet_listener.dart
+++ b/pkg/front_end/lib/src/fasta/source/diet_listener.dart
@@ -514,10 +514,6 @@ class DietListener extends StackListener {
       bool allowAbstract = asyncModifier == AsyncMarker.Sync;
       parser.parseFunctionBody(token, isExpression, allowAbstract);
       var body = listener.pop();
-      if (listener.stack.length == 2) {
-        listener.pop(); // constructor initializers
-        listener.pop(); // separator before constructor initializers
-      }
       listener.checkEmpty(token.charOffset);
       listener.finishFunction(formals, asyncModifier, body);
     } on InputError {