Include ':' before constructor separators into AST with Fasta.

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 0b7b385aeceee14412a2055a184a67c73e8eb74d..51b1e3632d065ebf6d70db604796972b29a99c3c 100644
--- a/pkg/front_end/lib/src/fasta/source/diet_listener.dart
+++ b/pkg/front_end/lib/src/fasta/source/diet_listener.dart
@@ -493,8 +493,9 @@ class DietListener extends StackListener {
       bool allowAbstract = asyncModifier == AsyncMarker.Sync;
       parser.parseFunctionBody(token, isExpression, allowAbstract);
       var body = listener.pop();
-      if (listener.stack.length == 1) {
+      if (listener.stack.length == 2) {
         listener.pop(); // constructor initializers
+        listener.pop(); // separator before constructor initializers
       }
       listener.checkEmpty(token.charOffset);
       listener.finishFunction(formals, asyncModifier, body);