Create ShareableFileReference on IO thread

webkit/fileapi/file_system_file_util.h

Index: webkit/fileapi/file_system_file_util.h
diff --git a/webkit/fileapi/file_system_file_util.h b/webkit/fileapi/file_system_file_util.h
index e1c98fae6fb8d56a5ac0b6256ff10058df68efec..8205dfd5148736c6d511eddef34a4f7587bf7c4d 100644
--- a/webkit/fileapi/file_system_file_util.h
+++ b/webkit/fileapi/file_system_file_util.h
@@ -46,6 +46,20 @@ class FILEAPI_EXPORT FileSystemFileUtil {
     virtual bool IsDirectory() = 0;
   };
 
+  // A policy flag for CreateSnapshotFile.
+  enum SnapshotFilePolicy {
+    kSnapshotFileUnknown,
+
+    // The implementation just uses the local file as the snapshot file.
+    // The FileAPI backend does nothing on the returned file.
+    kSnapshotFileLocal,
+
+    // The implementation returns a temporary file as the snapshot file.
+    // The FileAPI backend takes care of the lifetime of the returned file
+    // and will delete when the last reference of the file is dropped.
+    kSnapshotFileTemporary,
+  };
+
   class EmptyFileEnumerator : public AbstractFileEnumerator {
     virtual FilePath Next() OVERRIDE { return FilePath(); }
     virtual int64 Size() OVERRIDE { return 0; }
@@ -183,20 +197,16 @@ class FILEAPI_EXPORT FileSystemFileUtil {
   // temporary snapshot file which holds the file data and return
   // the metadata of the temporary file.
   //
-  // |result| is the return code of the operation.
   // |file_info| is the metadata of the snapshot file created.
   // |platform_path| is the path to the snapshot file created.
-  //
-  // The implementation can optionally return a file reference
-  // to let the fileapi backend manage the lifetime of the returned
-  // snapshot file. Otherwise it is ok to return NULL.
-  // Please see the comment for ShareableFileReference for details.
-  virtual scoped_refptr<webkit_blob::ShareableFileReference>
-      CreateSnapshotFile(FileSystemOperationContext* context,
-                         const FileSystemURL& url,
-                         base::PlatformFileError* result,
-                         base::PlatformFileInfo* file_info,
-                         FilePath* platform_path) = 0;
+  // |policy| should indicate the policy how the fileapi backend
+  // should handle the returned file.
+  virtual base::PlatformFileError CreateSnapshotFile(
+      FileSystemOperationContext* context,
+      const FileSystemURL& url,
+      base::PlatformFileInfo* file_info,
+      FilePath* platform_path,
+      SnapshotFilePolicy* policy) = 0;
 
  protected:
   FileSystemFileUtil() {}