[SyncFS] Show if a tracker is demoted or not in chrome://syncfs-internals

chrome/browser/sync_file_system/drive_backend/metadata_database_index_on_disk.cc

Index: chrome/browser/sync_file_system/drive_backend/metadata_database_index_on_disk.cc
diff --git a/chrome/browser/sync_file_system/drive_backend/metadata_database_index_on_disk.cc b/chrome/browser/sync_file_system/drive_backend/metadata_database_index_on_disk.cc
index 8d352328505f0d164930387784628d54b96b7103..8e44f75f059009bbf0f397fe15366f145867cb28 100644
--- a/chrome/browser/sync_file_system/drive_backend/metadata_database_index_on_disk.cc
+++ b/chrome/browser/sync_file_system/drive_backend/metadata_database_index_on_disk.cc
@@ -525,6 +525,11 @@ bool MetadataDatabaseIndexOnDisk::HasDemotedDirtyTracker() const {
   return StartsWithASCII(itr->key().ToString(), kDemotedDirtyIDKeyPrefix, true);
 }
 
+bool MetadataDatabaseIndexOnDisk::IsDemotedDirtyTracker(
+    int64 tracker_id) const {
+  return DBHasKey(GenerateDemotedDirtyIDKey(tracker_id));
+}
+
 void MetadataDatabaseIndexOnDisk::PromoteDemotedDirtyTracker(int64 tracker_id) {
   std::string demoted_key = GenerateDemotedDirtyIDKey(tracker_id);
 
@@ -1127,7 +1132,7 @@ void MetadataDatabaseIndexOnDisk::DeactivateInTrackerIDSetWithPrefix(
   }
 }
 
-bool MetadataDatabaseIndexOnDisk::DBHasKey(const std::string& key) {
+bool MetadataDatabaseIndexOnDisk::DBHasKey(const std::string& key) const {
   scoped_ptr<LevelDBWrapper::Iterator> itr(db_->NewIterator());
   itr->Seek(key);
   return itr->Valid() && (itr->key() == key);