Separate gathering Delta changes and validation.

pkg/analyzer/test/src/context/cache_test.dart

Index: pkg/analyzer/test/src/context/cache_test.dart
diff --git a/pkg/analyzer/test/src/context/cache_test.dart b/pkg/analyzer/test/src/context/cache_test.dart
index 1b2db037d09e0c6221812de335c56f15b7a7980f..d3ac2417e5b795798fe01d989d206c859ad676f3 100644
--- a/pkg/analyzer/test/src/context/cache_test.dart
+++ b/pkg/analyzer/test/src/context/cache_test.dart
@@ -1209,6 +1209,15 @@ class _KeepContinueDelta implements Delta {
   _KeepContinueDelta(this.source, this.keepDescriptor);
 
   @override
+  bool gatherChanges(InternalAnalysisContext context, AnalysisTarget target,
+      ResultDescriptor descriptor, Object value) {
+    return false;
+  }
+
+  @override
+  void gatherEnd() {}
+
+  @override
   DeltaResult validate(InternalAnalysisContext context, AnalysisTarget target,
       ResultDescriptor descriptor, Object value) {
     if (descriptor == keepDescriptor) {