[base] Prepare //components/sync for Value::GetList() switch

Value::GetList() will soon stop returning references to the underlying
vector. Instead it will return a thin wrapper that only allows iteration
and member access. This change prepares //components/sync* for this
switch.

Bug: 646113
Change-Id: I65cfed19643ddebd1db2dfb159493ab0c039b4a9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1887695
Commit-Queue: Jan Wilken Dörrie <jdoerrie@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710985}

components/sync_device_info/device_info_prefs.cc

@@ -101,15 +101,13 @@ bool DeviceInfoPrefs::IsRecentLocalCacheGuid(
 void DeviceInfoPrefs::AddLocalCacheGuid(const std::string& cache_guid) {
   ListPrefUpdate update_cache_guids(pref_service_,
                                     kDeviceInfoRecentGUIDsWithTimestamps);
-  base::Value::ListStorage* recent_local_cache_guids =
-      &(update_cache_guids.Get()->GetList());
 
-  for (auto it = recent_local_cache_guids->begin();
-       it != recent_local_cache_guids->end(); it++) {
+  for (auto it = update_cache_guids->GetList().begin();
+       it != update_cache_guids->GetList().end(); it++) {
     if (MatchesGuidInDictionary(*it, cache_guid)) {
       // Remove it from the list, to be reinserted below, in the first
       // position.
-      recent_local_cache_guids->erase(it);
+      update_cache_guids->EraseListIter(it);
       break;
     }
   }
@@ -120,36 +118,25 @@ void DeviceInfoPrefs::AddLocalCacheGuid(const std::string& cache_guid) {
       kTimestampKey,
       base::Value(clock_->Now().ToDeltaSinceWindowsEpoch().InDays()));
 
-  recent_local_cache_guids->emplace(recent_local_cache_guids->begin(),
-                                    std::move(new_entry));
+  update_cache_guids->Insert(update_cache_guids->GetList().begin(),
+                             std::move(new_entry));
 
-  while (recent_local_cache_guids->size() > kMaxLocalCacheGuidsStored) {
-    recent_local_cache_guids->pop_back();
+  while (update_cache_guids->GetList().size() > kMaxLocalCacheGuidsStored) {
+    update_cache_guids->EraseListIter(update_cache_guids->GetList().end() - 1);
   }
 }
 
 void DeviceInfoPrefs::GarbageCollectExpiredCacheGuids() {
   ListPrefUpdate update_cache_guids(pref_service_,
                                     kDeviceInfoRecentGUIDsWithTimestamps);
-  base::Value::ListStorage* recent_local_cache_guids =
-      &(update_cache_guids.Get())->GetList();
-
-  for (auto it = recent_local_cache_guids->begin();
-       it != recent_local_cache_guids->end(); it++) {
-    base::Optional<int> days_since_epoch = it->FindIntKey(kTimestampKey);
+  update_cache_guids->EraseListValueIf([this](const auto& dict) {
+    base::Optional<int> days_since_epoch = dict.FindIntKey(kTimestampKey);
     const base::Time creation_time =
         days_since_epoch ? base::Time::FromDeltaSinceWindowsEpoch(
                                base::TimeDelta::FromDays(*days_since_epoch))
                          : base::Time::Min();
-    if (creation_time < clock_->Now() - kMaxTimeDeltaLocalCacheGuidsStored) {
-      // Because the list of cache_guid prefs is maintained to be in reverse
-      // chronological order (from the newest cache guid to the oldest), it
-      // is safe to remove all of the entries after one that is found to be
-      // expired.
-      recent_local_cache_guids->erase(it, recent_local_cache_guids->end());
-      return;
-    }
-  }
+    return creation_time < clock_->Now() - kMaxTimeDeltaLocalCacheGuidsStored;
+  });
 }
 
 }  // namespace syncer

components/sync_device_info/device_info_prefs_unittest.cc

@@ -6,6 +6,7 @@
 
 #include "base/strings/stringprintf.h"
 #include "base/test/simple_test_clock.h"
+#include "base/values.h"
 #include "components/prefs/pref_registry_simple.h"
 #include "components/prefs/scoped_user_pref_update.h"
 #include "components/prefs/testing_pref_service.h"
@@ -31,13 +32,11 @@ TEST_F(DeviceInfoPrefsTest, ShouldMigrateFromObsoletePref) {
 
   ListPrefUpdate cache_guids_update(&pref_service_,
                                     kObsoleteDeviceInfoRecentGUIDs);
-  base::Value::ListStorage* recent_local_cache_guids =
-      &cache_guids_update.Get()->GetList();
 
-  recent_local_cache_guids->emplace(recent_local_cache_guids->begin(),
-                                    base::Value("old_guid1"));
-  recent_local_cache_guids->emplace(recent_local_cache_guids->begin(),
-                                    base::Value("old_guid2"));
+  cache_guids_update->Insert(cache_guids_update->GetList().begin(),
+                             base::Value("old_guid1"));
+  cache_guids_update->Insert(cache_guids_update->GetList().begin(),
+                             base::Value("old_guid2"));
 
   ASSERT_FALSE(device_info_prefs_.IsRecentLocalCacheGuid("old_guid1"));
   ASSERT_FALSE(device_info_prefs_.IsRecentLocalCacheGuid("old_guid2"));

components/sync_preferences/pref_model_associator.cc

@@ -322,10 +322,9 @@ std::unique_ptr<base::Value> PrefModelAssociator::MergeListValues(
   DCHECK(to_value.type() == base::Value::Type::LIST);
 
   base::Value result = to_value.Clone();
-  base::Value::ListStorage& list = result.GetList();
   for (const auto& value : from_value.GetList()) {
-    if (!base::Contains(list, value))
-      list.emplace_back(value.Clone());
+    if (!base::Contains(result.GetList(), value))
+      result.Append(value.Clone());
   }
 
   return base::Value::ToUniquePtrValue(std::move(result));