[Sync] Make children messages of UserEventSpecifics' consistent use event suffix.

components/sync/protocol/user_event_specifics.proto

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // Sync protocol datatype extension for user events.
 
 // Update proto_value_conversions{.h,.cc,_unittest.cc} if you change
 // any fields in this file.
 
 syntax = "proto2";
 
 option optimize_for = LITE_RUNTIME;
 
 package sync_pb;
 
-message FieldTrialEvent {
-  message FieldTrial {
+message FieldTrial {
+  message FieldTrialPair {
     optional fixed32 name_id = 1;
     optional fixed32 group_id = 2;
   }
-  repeated FieldTrial field_trials = 1;
+  repeated FieldTrialPair field_trial_pairs = 1;
 }
 
 // Language detection output.
 message LanguageDetection {
   message Language {
     // ISO 639 language code will be used.
     optional string language_code = 1;
     // Whether the detected language is reliable, note this is determined by
     // the CLD3.
     optional bool is_reliable = 2;
@@ skipping 49 matching lines @@
   // On startup we generate a new random id to identify which FieldTrialEvents
   // other events belonged to.
   optional fixed64 session_id = 3;
 
   // 4-7 reserved for future scalars.
 
   // Used for testing and debugging EventLog system.
   message Test {}
 
   oneof event {
-    Test test = 8;
-    FieldTrialEvent field_trial_event = 9;
-    LanguageDetection language_detection = 10;
-    Translation translation = 11;
+    Test test_event = 8;
+    FieldTrial field_trial_event = 9;
+    LanguageDetection language_detection_event = 10;
+    Translation translation_event = 11;
   }
 }