This patch changes the behavior of the downloads.download API's saveAs option. Previously, the behavior when neither value is provided (the "default behavior") was not defined by our documentation or Chrome's. Now, the default behavior is changing to rely on the Firefox "Save As" pref (browser.download.useDownloadDir). If Firefox is configured to open the "Save As" dialog for all downloads (browser.download.useDownloadDir == false), that behavior will be the default for the downloads.download API. Otherwise, the default behavior will be not to show the dialog.
This patch also moves some test functionality out of test_chrome_ext_downloads_saveAs.html. Previously, that test would test the saveAs option and also the conflictAction:"uniquify" option. In order to add testing for the new default behavior, it was necessary to move the testing of the conflictAction:"uniquify" option to a new test: test_chrome_ext_downloads_uniquify.html
MozReview-Commit-ID: u6VA4kexlr