Pass 'classKeyword' to endClassDeclaratio() and endNamedMixinApplication().

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 b611c770f6bdcf838dc78a941d494ea137a48790..4b4f7f116c0ae89e6df9c83bb9fa9fc27b059dd0 100644
--- a/pkg/front_end/lib/src/fasta/source/diet_listener.dart
+++ b/pkg/front_end/lib/src/fasta/source/diet_listener.dart
@@ -447,7 +447,8 @@ class DietListener extends StackListener {
 
   @override
   void endClassDeclaration(int interfacesCount, Token beginToken,
-      Token extendsKeyword, Token implementsKeyword, Token endToken) {
+      Token classKeyword, Token extendsKeyword, Token implementsKeyword,
+      Token endToken) {
     debugEvent("ClassDeclaration");
     checkEmpty(beginToken.charOffset);
   }
@@ -462,11 +463,11 @@ class DietListener extends StackListener {
 
   @override
   void endNamedMixinApplication(
-      Token classKeyword, Token equals, Token implementsKeyword,
-      Token endToken) {
+      Token beginToken, Token classKeyword, Token equals,
+      Token implementsKeyword, Token endToken) {
     debugEvent("NamedMixinApplication");
     pop(); // Name.
-    checkEmpty(classKeyword.charOffset);
+    checkEmpty(beginToken.charOffset);
   }
 
   @override