[SyncFS] Run RemoteToLocalSyncer as a background task

BUG=344769

Review URL: https://codereview.chromium.org/554213002

Cr-Commit-Position: refs/heads/master@{#296356}

chrome/browser/sync_file_system/drive_backend/local_to_remote_syncer.cc

@@ -290,7 +290,7 @@ void LocalToRemoteSyncer::ContinueAsBackgroundTask(
   //   and may delete FileTracker.  So, ensure |change_id| is not changed and
   //   check if FileTracker still exists.
   // - For UninstallAppTask, it may also delete FileMetadata and FileTracker.
-  //   And also, check if FileTracker still exists.
+  //   Check if FileTracker still exists.
   // - Others, SyncEngineInitializer and RegisterAppTask doesn't affect to
   //   LocalToRemoteSyncer.
   if (remote_file_tracker_) {
@@ -663,8 +663,7 @@ void LocalToRemoteSyncer::DidUploadNewFile(
   SyncCompleted(token.Pass(), status);
 }
 
-void LocalToRemoteSyncer::CreateRemoteFolder(
-    scoped_ptr<SyncTaskToken> token) {
+void LocalToRemoteSyncer::CreateRemoteFolder(scoped_ptr<SyncTaskToken> token) {
   DCHECK(remote_parent_folder_tracker_);
 
   base::FilePath title = storage::VirtualPath::BaseName(target_path_);

chrome/browser/sync_file_system/drive_backend/remote_to_local_syncer.h

@@ -12,6 +12,7 @@
 #include "base/memory/weak_ptr.h"
 #include "chrome/browser/sync_file_system/drive_backend/metadata_database.pb.h"
 #include "chrome/browser/sync_file_system/drive_backend/sync_task.h"
+#include "chrome/browser/sync_file_system/drive_backend/sync_task_manager.h"
 #include "chrome/browser/sync_file_system/remote_change_processor.h"
 #include "chrome/browser/sync_file_system/sync_action.h"
 #include "chrome/browser/sync_file_system/sync_callbacks.h"
@@ -41,6 +42,8 @@ class SyncEngineContext;
 
 class RemoteToLocalSyncer : public SyncTask {
  public:
+  typedef SyncTaskManager::Continuation Continuation;
+
   // Conflicting trackers will have low priority for RemoteToLocalSyncer so that
   // it should be resolved by LocatToRemoteSyncer.
   explicit RemoteToLocalSyncer(SyncEngineContext* sync_context);
@@ -102,6 +105,11 @@ class RemoteToLocalSyncer : public SyncTask {
   //   - Dispatch to HandleOfflineSolvable()
   void ResolveRemoteChange(scoped_ptr<SyncTaskToken> token);
 
+  void MoveToBackground(scoped_ptr<SyncTaskToken> token,
+                        const Continuation& continuation);
+  void ContinueAsBackgroundTask(const Continuation& continuation,
+                                scoped_ptr<SyncTaskToken> token);
+
   // Handles missing remote metadata case.
   // Fetches remote metadata and updates MetadataDatabase by that.  The sync
   // operation itself will be deferred to the next sync round.
@@ -132,8 +140,6 @@ class RemoteToLocalSyncer : public SyncTask {
   void DidPrepareForFolderUpdate(scoped_ptr<SyncTaskToken> token,
                                  SyncStatusCode status);
 
-  void HandleSyncRootDeletion(scoped_ptr<SyncTaskToken> token);
-
   // Handles deleted remote file.  Needs Prepare() call.
   // If the deleted tracker is the sync-root:
   //  - TODO(tzik): Needs special handling.
@@ -150,6 +156,8 @@ class RemoteToLocalSyncer : public SyncTask {
   void DidPrepareForDeletion(scoped_ptr<SyncTaskToken> token,
                              SyncStatusCode status);
 
+  void HandleFileMove(scoped_ptr<SyncTaskToken> token);
+
   // Handles new file.  Needs Prepare() call.
   void HandleContentUpdate(scoped_ptr<SyncTaskToken> token);