Implement DownloadHandler actually matching CEF3 API

[jornh]

Background:

• google group thread linking to old/new API
• and amaitland@41e4b36#comments

[amaitland]

Having a look at the updated API now, unfortunately I don't think Task is viable as it stands, which is a real shame.
It would appear that OnDownloadUpdated may potentially be called multiple times (For me, it happens once even before OnBeforeDownload which I think is rather strange).

[amaitland]

I've pushed https://github.com/amaitland/CefSharp/tree/feature/DownloadHandler which is a very rough and ready implementation. I've created a DownloadItem class which is used to expose a lot more info about the Download. I'm not 100% happy with the code, so I'm not raising a PR, just publishing as a discussion point. Feel free to push any changes to the branch!

I made some quick and dirty changes to the WPF example to get it running, so should just be able to launch and try download a file.

[amaitland]

public virtual void OnDownloadUpdated( CefRefPtr< CefBrowser > browser, CefRefPtr< CefDownloadItem > download_item, CefRefPtr< CefDownloadItemCallback > callback );

Called when a download's status or progress information has been updated. This may be called multiple times before and after OnBeforeDownload(). Execute |callback| either asynchronously or in this method to cancel the download if desired. Do not keep a reference to |download_item| outside of this method.

I find it strange that OnDownloadUpdated is called multiple times before OnBeforeDownload is called, it is however expected behavior, so I'm a little less puzzled in some ways and a little more puzzled in others! lol

[JanEggers]

i hope i can still taskify it but i didnt look into it yet.

async, ability to cancel screams for task. and put the progress in Task.AsyncState....

i will have a look at the weekend.

[amaitland]

@JanEggers If you've got time then any input would be greatly appreciated!

[perlun]

@JanEggers, sounds really good! Did you have any progress on this one?

[JanEggers]

just short.

the downloadhandler seems to be called by cef so ist not what i initially thought. so for now Task isnt that easy to implement.

i thought there would be a download method in ChromiumWebBrowser which could return a task

[amaitland]

OnDownloadUpdated and OnBeforeDownload are more like event handlers so I think we just expose them as per normal for now. Pretty close to being there with amaitland@bc50929

[perlun]

Any PR created for that one? Or is it still too much of WIP at the moment?

[amaitland]

Still needs some work. Thoughts on the best way to expose CefDownloadItem? This is what I've got so far amaitland@bc50929#diff-522027d07c9dc847368e881ff11f6ff3R55
Need to go over the API one more time and make sure I've got everything covered. I'll try and get onto that sometime today.