Adding previews information to PLM UKM

services/metrics/public/cpp/ukm_recorder.h

Index: services/metrics/public/cpp/ukm_recorder.h
diff --git a/services/metrics/public/cpp/ukm_recorder.h b/services/metrics/public/cpp/ukm_recorder.h
index 5fefaaeec115bb26d64470ffa9acea979d314329..0d84abd380139ea95dc54c01d78ecde2a0c67c3a 100644
--- a/services/metrics/public/cpp/ukm_recorder.h
+++ b/services/metrics/public/cpp/ukm_recorder.h
@@ -55,6 +55,10 @@ class PasswordManagerMetricsRecorder;
 class PasswordFormMetricsRecorder;
 }  // namespace password_manager
 
+namespace previews {
+class PreviewsUKMObserver;
+}
+
 namespace ukm {
 
 class UkmEntryBuilder;
@@ -110,6 +114,7 @@ class METRICS_EXPORT UkmRecorder {
   friend content::RenderWidgetHostLatencyTracker;
   friend password_manager::PasswordManagerMetricsRecorder;
   friend password_manager::PasswordFormMetricsRecorder;
+  friend previews::PreviewsUKMObserver;
   friend resource_coordinator::CoordinationUnitManager;
   FRIEND_TEST_ALL_PREFIXES(UkmServiceTest, AddEntryWithEmptyMetrics);
   FRIEND_TEST_ALL_PREFIXES(UkmServiceTest, EntryBuilderAndSerialization);