Bug 277493 – UIDelegate method to dissallow FileUpload panel for an arbitrary frame

• Status: NEW
• Component: WebKit API

For security reasons one may want to forbid file uploads on certain domains. On MacOS this could be achieved by checking `frame` in the implementation of `runOpenPanelWithParameters`. But this method is unavailable on other platforms.
I don't think it will be practical to add `runOpenPanelWithParameters` on iOS, but the same goal could be achieved by adding an optional method:
```
- (void)webView:(WKWebView *)webView canRunOpenPanelWithParameters:(WKOpenPanelParameters *)parameters initiatedByFrame:(WKFrameInfo *)frame completionHandler:(void (^)(BOOL allow))completionHandler;
```
which is called before showing the FileUpload panel.
And it could be further enhanced with
```
- (void)webView:(WKWebView *)webView filterOpenPanelResults:(NSArray<NSURL *> * URLs)urls forFrame:(WKFrameInfo *)frame completionHandler:(void (^)(NSArray<NSURL *> * _Nullable URLs))completionHandler;
```
which is called after the FileUpload panel is dismissed and can be used to filter selected files based on their urls (for example by extension).

[Radar WebKit Bug Importer]

<rdar://problem/133475175>