Auto merge of #11931 - izgzhen:fix-html-input-element, r=Manishearth

Fix file-type input element

A simple fix to put `inputElem.files` online

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors

<!-- Either: -->
- [x] There are tests for these changes

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="35" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/11931)
<!-- Reviewable:end -->

components/script/dom/htmlinputelement.rs

@@ -302,6 +302,14 @@ impl HTMLInputElementMethods for HTMLInputElement {
         self.form_owner()
     }
 
+    // https://html.spec.whatwg.org/multipage/#dom-input-files
+    fn GetFiles(&self) -> Option<Root<FileList>> {
+        match self.filelist.get() {
+            Some(ref fl) => Some(fl.clone()),
+            None => None,
+        }
+    }
+
     // https://html.spec.whatwg.org/multipage/#dom-input-defaultchecked
     make_bool_getter!(DefaultChecked, "checked");
 
@@ -796,6 +804,12 @@ impl VirtualMethods for HTMLInputElement {
                             el.set_read_write_state(false);
                         }
 
+                        if new_type == InputType::InputFile {
+                            let window = window_from_node(self);
+                            let filelist = FileList::new(window.r(), vec![]);
+                            self.filelist.set(Some(&filelist));
+                        }
+
                         let new_value_mode = self.value_mode();
 
                         match (&old_value_mode, old_idl_value.is_empty(), new_value_mode) {

components/script/dom/webidls/HTMLInputElement.webidl

@@ -13,7 +13,7 @@ interface HTMLInputElement : HTMLElement {
            attribute DOMString dirName;
            attribute boolean disabled;
   readonly attribute HTMLFormElement? form;
-  //readonly attribute FileList? files;
+  readonly attribute FileList? files;
              attribute DOMString formAction;
              attribute DOMString formEnctype;
              attribute DOMString formMethod;