Add ephemeral_id in cast_logs.

Bug: 168739659
Test: CQ
Change-Id: Ib08ee3223f32318653b3bd6924fedf718887bb7b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2453916
Commit-Queue: Sunil Kumar <skx@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816284}

third_party/metrics_proto/README.chromium

 Name: Metrics Protos
 Short Name: metrics_proto
 URL: This is the canonical public repository
-Version: 333731142
-Date: 2020/09/25 UTC
+Version: 336717828
+Date: 2020/10/12 UTC
 License: BSD
 Security Critical: Yes
 

third_party/metrics_proto/cast_logs.proto

@@ -11,7 +11,7 @@ option java_outer_classname = "CastLogsProtos";
 
 package metrics;  // Cast-enabled device specific log data included in ChromeUserMetricsExtension.
 
-// Next tag: 7
+// Next tag: 8
 message CastLogsProto {
   // Cast specific device information.
   // Next tag: 7
@@ -331,4 +331,8 @@ message CastLogsProto {
   optional CastDeviceMutableInfo cast_device_mutable_info = 5;
 
   optional fixed64 receiver_metrics_id = 6;
+
+  // This ID is only ever recorded for Google-internal users (dogfooders). It
+  // is never recorded for external users."
+  optional uint64 ephemeral_id = 7;
 }