Stop defensively copying AST structures before resolution

pkg/analysis_server/test/analysis/notification_implemented_test.dart

Index: pkg/analysis_server/test/analysis/notification_implemented_test.dart
diff --git a/pkg/analysis_server/test/analysis/notification_implemented_test.dart b/pkg/analysis_server/test/analysis/notification_implemented_test.dart
index 5898daf4ee5ca4d14e36c04db9ec10df9928ff9f..fc72b72d566babe7ebf6e0551a59cea4fa1f69f1 100644
--- a/pkg/analysis_server/test/analysis/notification_implemented_test.dart
+++ b/pkg/analysis_server/test/analysis/notification_implemented_test.dart
@@ -37,6 +37,9 @@ class AnalysisNotificationImplementedTest extends AbstractAnalysisTest {
     if (length == -1) {
       length = findIdentifierLength(search);
     }
+    if (implementedClasses == null) {
+      fail('No notification of impemented classes was received');
+    }
     for (ImplementedClass clazz in implementedClasses) {
       if (clazz.offset == offset && clazz.length == length) {
         return;
@@ -57,6 +60,9 @@ class AnalysisNotificationImplementedTest extends AbstractAnalysisTest {
     if (length == -1) {
       length = findIdentifierLength(search);
     }
+    if (implementedMembers == null) {
+      fail('No notification of impemented members was received');
+    }
     for (ImplementedMember member in implementedMembers) {
       if (member.offset == offset && member.length == length) {
         return;
@@ -77,6 +83,9 @@ class AnalysisNotificationImplementedTest extends AbstractAnalysisTest {
     if (length == -1) {
       length = findIdentifierLength(search);
     }
+    if (implementedMembers == null) {
+      fail('No notification of impemented members was received');
+    }
     for (ImplementedMember member in implementedMembers) {
       if (member.offset == offset) {
         fail('Unexpected implemented member at $offset'