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 33fa404e16ba65fb54a7878e28f2fee21e3df6d6..05fe2cf63b9e3ad623fb91049200e9650f61b20d 100644
--- a/lib/compiler/implementation/scanner/parser.dart
+++ b/lib/compiler/implementation/scanner/parser.dart
@@ -429,10 +429,13 @@ 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;