Add SyncableService::WaitUntilReadyToSync() for autofill profile

The codepath is unreachable because we don't exercise it in the
old, directory-based architecture. This datatype hasn't been
integrated into pseudo-USS, so there's no need to implement the
wait.

This CL was uploaded by git cl split.

R=melandory@chromium.org

Change-Id: Idd75a1dc27d097ea9620a1ea5dc9e6d9952f923f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1545391
Commit-Queue: Tatiana Gornak <melandory@chromium.org>
Reviewed-by: Tatiana Gornak <melandory@chromium.org>
Auto-Submit: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#646265}

components/autofill/core/browser/webdata/autofill_profile_syncable_service.cc

@@ -94,6 +94,12 @@ AutofillProfileSyncableService::FromWebDataService(
 AutofillProfileSyncableService::AutofillProfileSyncableService()
     : webdata_backend_(nullptr), scoped_observer_(this) {}
 
+void AutofillProfileSyncableService::WaitUntilReadyToSync(
+    base::OnceClosure done) {
+  // Not used in the legacy directory-based architecture.
+  NOTREACHED();
+}
+
 syncer::SyncMergeResult
 AutofillProfileSyncableService::MergeDataAndStartSyncing(
     syncer::ModelType type,

components/autofill/core/browser/webdata/autofill_profile_syncable_service.h

@@ -70,6 +70,7 @@ class AutofillProfileSyncableService
   static syncer::ModelType model_type() { return syncer::AUTOFILL_PROFILE; }
 
   // syncer::SyncableService implementation.
+  void WaitUntilReadyToSync(base::OnceClosure done) override;
   syncer::SyncMergeResult MergeDataAndStartSyncing(
       syncer::ModelType type,
       const syncer::SyncDataList& initial_sync_data,