Implement file-type functionalities in htmlinputelement and related

Changes include:
- Implement file selection and other DOM behaviours in htmlinputelement
- Integrate IpcSender<FileManagerThreadMsg> into ResourceThreads
- Improve filemanager_thread, including adding type_string field to SelectedFile
- Improve interfaces in FileList/File/Blob to accommodate the above changes

components/script/dom/filelist.rs

@@ -27,8 +27,10 @@ impl FileList {
     }
 
     #[allow(unrooted_must_root)]
-    pub fn new(window: &Window, files: Vec<JS<File>>) -> Root<FileList> {
-        reflect_dom_object(box FileList::new_inherited(files), GlobalRef::Window(window), FileListBinding::Wrap)
+    pub fn new(window: &Window, files: Vec<Root<File>>) -> Root<FileList> {
+        reflect_dom_object(box FileList::new_inherited(files.iter().map(|r| JS::from_rooted(&r)).collect()),
+                           GlobalRef::Window(window),
+                           FileListBinding::Wrap)
     }
 }