[Sync] Extend device info specifics with invalidations token

This patch changes only Sync protocol. It extends device info specifics
to support sync invalidations with an invalidations token.

Bug: 1082117
Change-Id: I861bf0d959932b7270c626f7b3445cf5a40ac543
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2214887
Commit-Queue: Rushan Suleymanov <rushans@google.com>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#772655}

components/sync/protocol/device_info_specifics.proto

@@ -71,6 +71,9 @@ message DeviceInfoSpecifics {
   // excludes backgrounded apps on Android). Introduced in M81. The legacy
   // default was 1 day.
   optional int32 pulse_interval_in_minutes = 13;
+
+  // Device specific information for Sync invalidations.
+  optional InvalidationSpecificFields invalidation_fields = 14;
 }
 
 // Feature specific information about the device that is running a sync-enabled
@@ -137,3 +140,11 @@ message SharingSpecificFields {
   // Auth secret for message encryption [RFC8291] using Sharing sender ID.
   optional bytes sender_id_auth_secret_v2 = 10;
 }
+
+// Device specific information telling how to send invalidations to this device.
+message InvalidationSpecificFields {
+  // FCM registration token of device (using Sync sender ID).
+  optional string instance_id_token = 1;
+
+  // TODO(crbug.com/1082117): add data types list.
+}

components/sync/protocol/proto_visitors.h

@@ -326,6 +326,7 @@ VISIT_PROTO_FIELDS(const sync_pb::DeviceInfoSpecifics& proto) {
   VISIT(last_updated_timestamp);
   VISIT(feature_fields);
   VISIT(sharing_fields);
+  VISIT(invalidation_fields);
 }
 
 VISIT_PROTO_FIELDS(const sync_pb::FeatureSpecificFields& proto) {
@@ -528,6 +529,10 @@ VISIT_PROTO_FIELDS(const sync_pb::HistoryDeleteDirectives& proto) {
   VISIT(enabled);
 }
 
+VISIT_PROTO_FIELDS(const sync_pb::InvalidationSpecificFields& proto) {
+  VISIT(instance_id_token);
+}
+
 VISIT_PROTO_FIELDS(const sync_pb::KeystoreEncryptionFlags& proto) {
   VISIT(enabled);
 }