[Sync] Remove ModelError::IsSet() in favor of base::Optional.

components/reading_list/ios/reading_list_store_unittest.mm

 // Copyright 2016 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.
 
 #include "components/reading_list/ios/reading_list_store.h"
 
 #include <map>
 #include <set>
 
 #include "base/bind.h"
@@ skipping 202 matching lines @@
       entry.AsReadingListSpecifics();
 
   syncer::EntityData data;
   data.client_tag_hash = "http://read.example.com/";
   *data.specifics.mutable_reading_list() = *specifics;
 
   remote_input["http://read.example.com/"] = data.PassToPtr();
 
   std::unique_ptr<syncer::MetadataChangeList> metadata_changes(
       reading_list_store_->CreateMetadataChangeList());
-  const syncer::ModelError error = reading_list_store_->MergeSyncData(
-      std::move(metadata_changes), remote_input);
+  auto error = reading_list_store_->MergeSyncData(std::move(metadata_changes),

[skym, 2017/01/10 16:24:41]

Why are these error variables being stored? They're never used. Should they be
checked?

[maxbogue, 2017/01/10 17:53:50]

I don't know; I'll ask Olivier about it.

+                                                  remote_input);
   AssertCounts(0, 0, 1, 0, 0);
   EXPECT_EQ(sync_added_.size(), 1u);
   EXPECT_EQ(sync_added_.count("http://read.example.com/"), 1u);
   EXPECT_EQ(sync_added_["http://read.example.com/"], true);
 }
 
 TEST_F(ReadingListStoreTest, ApplySyncChangesOneAdd) {
   syncer::EntityDataMap remote_input;
   ReadingListEntry entry(GURL("http://read.example.com/"), "read title");
   entry.SetRead(true);
   std::unique_ptr<sync_pb::ReadingListSpecifics> specifics =
       entry.AsReadingListSpecifics();
   syncer::EntityData data;
   data.client_tag_hash = "http://read.example.com/";
   *data.specifics.mutable_reading_list() = *specifics;
 
   syncer::EntityChangeList add_changes;
 
   add_changes.push_back(syncer::EntityChange::CreateAdd(
       "http://read.example.com/", data.PassToPtr()));
-  syncer::ModelError error = reading_list_store_->ApplySyncChanges(
+  auto error = reading_list_store_->ApplySyncChanges(
       reading_list_store_->CreateMetadataChangeList(), add_changes);
   AssertCounts(0, 0, 1, 0, 0);
   EXPECT_EQ(sync_added_.size(), 1u);
   EXPECT_EQ(sync_added_.count("http://read.example.com/"), 1u);
   EXPECT_EQ(sync_added_["http://read.example.com/"], true);
 }
 
 TEST_F(ReadingListStoreTest, ApplySyncChangesOneMerge) {
   syncer::EntityDataMap remote_input;
   model_->AddEntry(GURL("http://unread.example.com/"), "unread title");
   base::test::ios::SpinRunLoopWithMinDelay(
       base::TimeDelta::FromMilliseconds(10));
 
   ReadingListEntry new_entry(GURL("http://unread.example.com/"),
                              "unread title");
   new_entry.SetRead(true);
   std::unique_ptr<sync_pb::ReadingListSpecifics> specifics =
       new_entry.AsReadingListSpecifics();
   syncer::EntityData data;
   data.client_tag_hash = "http://unread.example.com/";
   *data.specifics.mutable_reading_list() = *specifics;
 
   syncer::EntityChangeList add_changes;
   add_changes.push_back(syncer::EntityChange::CreateAdd(
       "http://unread.example.com/", data.PassToPtr()));
-  syncer::ModelError error = reading_list_store_->ApplySyncChanges(
+  auto error = reading_list_store_->ApplySyncChanges(
       reading_list_store_->CreateMetadataChangeList(), add_changes);
   AssertCounts(1, 0, 0, 0, 1);
   EXPECT_EQ(sync_merged_.size(), 1u);
   EXPECT_EQ(sync_merged_.count("http://unread.example.com/"), 1u);
   EXPECT_EQ(sync_merged_["http://unread.example.com/"], true);
 }
 
 TEST_F(ReadingListStoreTest, ApplySyncChangesOneIgnored) {
   // Read entry but with unread URL as it must update the other one.
   ReadingListEntry old_entry(GURL("http://unread.example.com/"),
                              "old unread title");
   old_entry.SetRead(true);
 
   base::test::ios::SpinRunLoopWithMinDelay(
       base::TimeDelta::FromMilliseconds(10));
   syncer::EntityDataMap remote_input;
   model_->AddEntry(GURL("http://unread.example.com/"), "new unread title");
   AssertCounts(0, 0, 0, 0, 0);
 
   std::unique_ptr<sync_pb::ReadingListSpecifics> specifics =
       old_entry.AsReadingListSpecifics();
   syncer::EntityData data;
   data.client_tag_hash = "http://unread.example.com/";
   *data.specifics.mutable_reading_list() = *specifics;
 
   syncer::EntityChangeList add_changes;
   add_changes.push_back(syncer::EntityChange::CreateAdd(
       "http://unread.example.com/", data.PassToPtr()));
-  syncer::ModelError error = reading_list_store_->ApplySyncChanges(
+  auto error = reading_list_store_->ApplySyncChanges(
       reading_list_store_->CreateMetadataChangeList(), add_changes);
   AssertCounts(1, 0, 0, 0, 1);
   EXPECT_EQ(sync_merged_.size(), 1u);
 }
 
 TEST_F(ReadingListStoreTest, ApplySyncChangesOneRemove) {
   syncer::EntityChangeList delete_changes;
   delete_changes.push_back(
       syncer::EntityChange::CreateDelete("http://read.example.com/"));
-  syncer::ModelError error = reading_list_store_->ApplySyncChanges(
+  auto error = reading_list_store_->ApplySyncChanges(
       reading_list_store_->CreateMetadataChangeList(), delete_changes);
   AssertCounts(0, 0, 0, 1, 0);
   EXPECT_EQ(sync_removed_.size(), 1u);
   EXPECT_EQ(sync_removed_.count("http://read.example.com/"), 1u);
 }
 
 TEST_F(ReadingListStoreTest, CompareEntriesForSync) {
   sync_pb::ReadingListSpecifics entryA;
   sync_pb::ReadingListSpecifics entryB;
   entryA.set_entry_id("http://foo.bar/");
@@ skipping 108 matching lines @@
     entryB.set_status(status_oder[index_a]);
     ExpectAB(entryA, entryB, true);
     ExpectAB(entryB, entryA, true);
     for (int index_b = index_a + 1; index_b < 3; index_b++) {
       entryB.set_status(status_oder[index_b]);
       ExpectAB(entryA, entryB, true);
       ExpectAB(entryB, entryA, false);
     }
   }
 }