Bug 923922, part 1 - Rename DirPickerBuildFileListTasks to DirPickerFileListBuilderTask. r=smaug
Bug 923922, part 2 - Allow DirPickerBuildFileListTasks to be cancelled, and cancel any in-progress DirPickerBuildFileListTasks when the user picks a new directory. r=smaug
Bug 923926 - Allow content authors to cancel the directory scan initiated when the user picks a directory. r=smaug
Bug 912492 - Clear HTMLInputElement.files immediately after a user picks a directory. r=smaug