Tests

1. Click on the extension button to trigger downloads.download from the background.
2. Click here to trigger downloads.download from here (in this tab)
3. Click here to trigger downloads.download in the background, calling from here.
4. Click here to trigger a download via <a download>.

Expectations

1. See download dialog from background page.
2. See download dialog from this tab.
3. See download dialog from background page.
4. See download dialog from this tab.