Sync: Small refactoring of Directory::CheckTreeInvariants.

The purpose of this change is to minimize chances of hitting
crbug/456029.

1) Call ModelTypeToRootTag only when the root folder could
potentially be created on the client i.e. model type is
defined in client EntitySpecifics and it is one of supported
model types.
2) Rename is_type_root_folder to is_client_creatable_type_root_folder
to make it clear that the checks are specific to client
created type root folders.
3) Narrow the scope of where is_client_creatable_type_root_folder
has to be calculated.

BUG=456029

Review URL: https://codereview.chromium.org/948113005

Cr-Commit-Position: refs/heads/master@{#317742}

sync/engine/directory_update_handler.cc

@@ -68,7 +68,7 @@ SyncerError DirectoryUpdateHandler::ProcessGetUpdatesResponse(
 
   // Auto-create permanent folder for the type if the progress marker
   // changes from empty to non-empty.
-  if (!IsTypeWithServerGeneratedRoot(type_) &&
+  if (IsTypeWithClientGeneratedRoot(type_) &&
       dir_->HasEmptyDownloadProgress(type_) &&
       IsValidProgressMarker(progress_marker)) {
     CreateTypeRoot(&trans);

sync/engine/syncer_util.cc

@@ -267,7 +267,7 @@ UpdateAttemptResponse AttemptToUpdateEntry(
       }
     } else {
       // new_parent is unset.
-      DCHECK(!IsTypeWithServerGeneratedRoot(type));
+      DCHECK(IsTypeWithClientGeneratedRoot(type));
     }
   } else if (entry->GetIsDir()) {
     Directory::Metahandles handles;

sync/internal_api/public/base/model_type.h

@@ -331,6 +331,10 @@ SYNC_EXPORT bool IsActOnceDataType(ModelType model_type);
 // created on the server during initial sync.
 SYNC_EXPORT bool IsTypeWithServerGeneratedRoot(ModelType model_type);
 
+// Returns true if root folder for |model_type| is created on the client when
+// that type is initially synced.
+SYNC_EXPORT bool IsTypeWithClientGeneratedRoot(ModelType model_type);
+
 // Returns set of model types that should be backed up before first sync.
 SYNC_EXPORT ModelTypeSet BackupTypes();
 

sync/syncable/directory.cc

@@ -1226,14 +1226,18 @@ bool Directory::CheckTreeInvariants(syncable::BaseTransaction* trans,
     int64 base_version = e.GetBaseVersion();
     int64 server_version = e.GetServerVersion();
     bool using_unique_client_tag = !e.GetUniqueClientTag().empty();
-    bool is_type_root_folder =
-        parentid.IsRoot() &&
-        e.GetUniqueServerTag() == ModelTypeToRootTag(e.GetModelType());
     if (CHANGES_VERSION == base_version || 0 == base_version) {
+      ModelType model_type = e.GetModelType();
+      bool is_client_creatable_type_root_folder =
+          parentid.IsRoot() &&
+          IsTypeWithClientGeneratedRoot(model_type) &&
+          e.GetUniqueServerTag() == ModelTypeToRootTag(model_type);
       if (e.GetIsUnappliedUpdate()) {
         // Must be a new item, or a de-duplicated unique client tag
+        // that was created both locally and remotely, or a type root folder
         // that was created both locally and remotely.
-        if (!(using_unique_client_tag || is_type_root_folder)) {
+        if (!(using_unique_client_tag ||
+              is_client_creatable_type_root_folder)) {
           if (!SyncAssert(e.GetIsDel(), FROM_HERE,
                           "The entry should have been deleted.", trans))
             return false;
@@ -1252,8 +1256,8 @@ bool Directory::CheckTreeInvariants(syncable::BaseTransaction* trans,
                           trans))
             return false;
         }
-        if (is_type_root_folder) {
-          // This must be a locally created type root folder
+        if (is_client_creatable_type_root_folder) {
+          // This must be a locally created type root folder.
           if (!SyncAssert(
                   !e.GetIsUnsynced(), FROM_HERE,
                   "Locally created type root folders should not be unsynced.",

sync/syncable/model_neutral_mutable_entry.cc

@@ -48,7 +48,7 @@ ModelNeutralMutableEntry::ModelNeutralMutableEntry(BaseWriteTransaction* trans,
                                                    CreateNewTypeRoot,
                                                    ModelType type)
     : Entry(trans), base_write_transaction_(trans) {
-  DCHECK(!IsTypeWithServerGeneratedRoot(type));
+  DCHECK(IsTypeWithClientGeneratedRoot(type));
   Entry same_type_root(trans, GET_TYPE_ROOT, type);
   kernel_ = NULL;
   if (same_type_root.good()) {

sync/syncable/model_type.cc

@@ -1187,4 +1187,9 @@ bool IsTypeWithServerGeneratedRoot(ModelType model_type) {
   return model_type == BOOKMARKS || model_type == NIGORI;
 }
 
+bool IsTypeWithClientGeneratedRoot(ModelType model_type) {
+  return IsRealDataType(model_type) &&
+         !IsTypeWithServerGeneratedRoot(model_type);
+}
+
 }  // namespace syncer