Spawn threads for requests in file manager and other style fixes

components/net_traits/blob_url_store.rs

@@ -13,6 +13,10 @@ pub enum BlobURLStoreError {
     InvalidFileID,
     /// Invalid URL origin
     InvalidOrigin,
+    /// Invalid entry content
+    InvalidEntry,
+    /// External error, from like file system, I/O etc.
+    External,
 }
 
 /// Blob URL store entry, a packaged form of Blob DOM object

components/net_traits/filemanager_thread.rs

@@ -136,7 +136,7 @@ pub enum FileManagerThreadMsg {
     AddSlicedEntry(SelectedFileId, RelativePos, IpcSender<Result<SelectedFileId, BlobURLStoreError>>, FileOrigin),
 
     /// Decrease reference count
-    DecRef(SelectedFileId, FileOrigin),
+    DecRef(SelectedFileId, FileOrigin, IpcSender<Result<(), BlobURLStoreError>>),
 
     /// Increase reference count
     IncRef(SelectedFileId, FileOrigin),