Add contextual information about identifiers to the parser listener API.

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

Index: pkg/front_end/lib/src/fasta/parser/listener.dart
diff --git a/pkg/front_end/lib/src/fasta/parser/listener.dart b/pkg/front_end/lib/src/fasta/parser/listener.dart
index 7407d212671373c341b19f7f82e3b142f0dcc3f5..0456fdd243c7d9145ae5ae1c5c32d4c5a23cfe6d 100644
--- a/pkg/front_end/lib/src/fasta/parser/listener.dart
+++ b/pkg/front_end/lib/src/fasta/parser/listener.dart
@@ -10,6 +10,8 @@ import '../util/link.dart' show Link;
 
 import 'error_kind.dart' show ErrorKind;
 
+import 'identifier_context.dart' show IdentifierContext;
+
 /// A parser event listener that does nothing except throw exceptions
 /// on parser errors.
 ///
@@ -712,7 +714,10 @@ class Listener {
     logEvent("FunctionTypedFormalParameter");
   }
 
-  void handleIdentifier(Token token) {
+  /// Handle an identifier token.
+  ///
+  /// [context] indicates what kind of construct the identifier appears in.
+  void handleIdentifier(Token token, IdentifierContext context) {
     logEvent("Identifier");
   }