[drag and drop] prevent default dnd behavior

[vince-fugnitto]

What it does

Fixes #674

• prevent default dnd (drag & drop) behavior when dragging a file from
  the filesystem into Theia. The default browser behavior meant that
  the application was replaced by the browser attempting to open the file
  as a URL.
• [minor] fix a few typos in the same file.

Tested

• tested in Chrome, Firefox and Safari

How to test

1. open a workspace
2. when no files are currently opened, attempt to drag a file from your filesystem into the application's main panel
3. the application should not be replaced with the browser attempting to open the file as a URL (in master this is the case
4. make sure that other dnd events (ex: explorer) still work correctly

Example

Additional Notes

In the future, we can attempt to open the file in an editor if possible, but looking at the current web API, obtaining the path of a file and opening it does not seem possible. Perhaps we can come up with a workaround as to download the file, store it temporarily, and then open it.

Review checklist

• as an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• as a reviewer, I agree to behave in accordance with the review guidelines

Signed-off-by: Vincent Fugnitto [email protected]

[akosyakov]

Please as part of verification check that it does not break d&d of file in the navigator, and parts in the debug view.

[vince-fugnitto]

Please as part of verification check that it does not break d&d of file in the navigator, and parts in the debug view.

I've verified the following cases in the explorer:

• dnd a file from my filesystem into a folder in the explorer
• dnd a file from one folder to another in the explorer
• also tested the same two scenarios in a multi-root workspace

How can I verify dnd in the debug view?

[akosyakov]

How can I verify dnd in the debug view?

Move parts, e.g. Variables after Breakpoints.

[vince-fugnitto]

How can I verify dnd in the debug view?

Move parts, e.g. Variables after Breakpoints.

Thanks, I confirmed it still works correctly.

[lmcbout]

LGTM
Tested on Ubuntu 16.04 with Chrome and Firefox

• D&D over the editor does not open the file and the browser remains in Theia
• D&D in explorer works well
• Cancel button in the progress dialog stops the transfer for large folder
  Tested on single and multi-root
  Code looks good