sync: Add pre-commit update avoidance mode + flag

sync/protocol/experiments_specifics.proto

 // Copyright (c) 2012 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 experimental feature flags.
 
 syntax = "proto2";
 
 option optimize_for = LITE_RUNTIME;
 option retain_unknown_fields = true;
@@ skipping 16 matching lines @@
   optional bool enabled = 1;
 }
 
 // Whether the favicon sync datatypes are enabled, and what parameters
 // they should operate under.
 message FaviconSyncFlags {
   optional bool enabled = 1;
   optional int32 favicon_sync_limit = 2 [default = 200];
 }
 
+// Flags for enabling the experimental no-precommit GU feature.
+message PreCommitUpdateAvoidanceFlags {
+  optional bool enabled = 1;
+}
+
 // Contains one flag or set of related flags.  Each node of the experiments type
 // will have a unique_client_tag identifying which flags it contains.  By
 // convention, the tag name should match the sub-message name.
 message ExperimentsSpecifics {
   optional KeystoreEncryptionFlags keystore_encryption = 1;
   optional HistoryDeleteDirectives history_delete_directives = 2;
   optional AutofillCullingFlags autofill_culling = 3;
   optional FaviconSyncFlags favicon_sync = 4;
+  optional PreCommitUpdateAvoidanceFlags pre_commit_update_avoidance = 5;
 }