Handle modifiers (abstract) on class nodes.

lib/compiler/implementation/scanner/parser.dart

Index: lib/compiler/implementation/scanner/parser.dart
diff --git a/lib/compiler/implementation/scanner/parser.dart b/lib/compiler/implementation/scanner/parser.dart
index 4f4f5ddba2aba43b2f61400ae36a5585d69f63d0..3b0c601fe81035370cee01acc2cbe652d926ebb5 100644
--- a/lib/compiler/implementation/scanner/parser.dart
+++ b/lib/compiler/implementation/scanner/parser.dart
@@ -385,10 +385,13 @@ class Parser {
   Token parseClass(Token token) {
     Token begin = token;
     listener.beginClassDeclaration(token);
+    int modifierCount = 0;
     if (optional('abstract', token)) {
-      // TODO(ahe): Notify listener about abstract modifier.
+      listener.handleModifier(token);
+      modifierCount++;
       token = token.next;
     }
+    listener.handleModifiers(modifierCount);
     token = parseIdentifier(token.next);
     token = parseTypeVariablesOpt(token);
     Token extendsKeyword;