dart:html lacks file system implementation API (missing constructors)

[DartBot]

This issue was originally filed by @financecoding

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This may be known already, constructors for using filesystem api does not exist in dart:html library.

[dgrove]

Set owner to @jacob314.
Added Area-UI, Triaged labels.

[DartBot]

This comment was originally written by @seaneagan

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I wonder if there is any possibility to be able to use the same File API which is currently within the server-side "dart:builtin" library, in "dart:html" as well ? Possibly separate it into a "dart:file" library which could be included in both "dart:html" and "dart:builtin".

[vsmenon]

Removed Area-UI label.
Added Area-DOM label.

[vsmenon]

Set owner to @vsmenon.
Added this to the M1 milestone.

[iposva-google]

Removed Area-DOM label.
Added Area-HTML label.

[vsmenon]

Removed the owner.

[blois]

Set owner to @blois.
Added Accepted label.

[blois]

The file system entry is via Window.webkitRequestFileSystem, creation of directories and files must go through that API.

Note that there are currently some bugs logged against this API, these issues are tracked by issue #3022.

I believe that the API in it's current form is functionally complete.

I split out the request for unify the File APIs into issue #4745.

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Added AsDesigned label.