Added an app-specific syncable Drive folder.
Added an app-specific syncable Drive folder.

Files created using DirectoryEntry.getFile will be stored in the correct directory on the user's Drive.

Also made syncFile call a callback when completed.
Also changed "method" to "function" in comments.
Also removed trailing whitespace and errant debugging logging.
liqingzhu/mobile-chrome-apps,hgl888/mobile-chrome-apps,guozanhua/mobile-chrome-apps,chirilo/mobile-chrome-apps,chirilo/mobile-chrome-apps,liqingzhu/mobile-chrome-apps,wudkj/mobile-chrome-apps,MobileChromeApps/mobile-chrome-apps,liqingzhu/mobile-chrome-apps,hgl888/mobile-chrome-apps,chirilo/mobile-chrome-apps,xiaoyanit/mobile-chrome-apps,hgl888/mobile-chrome-apps,hgl888/mobile-chrome-apps,xiaoyanit/mobile-chrome-apps,liqingzhu/mobile-chrome-apps,xiaoyanit/mobile-chrome-apps,hgl888/mobile-chrome-apps,wudkj/mobile-chrome-apps,hgl888/mobile-chrome-apps,guozanhua/mobile-chrome-apps,xiaoyanit/mobile-chrome-apps,wudkj/mobile-chrome-apps,guozanhua/mobile-chrome-apps,guozanhua/mobile-chrome-apps,hgl888/mobile-chrome-apps,wudkj/mobile-chrome-apps,MobileChromeApps/mobile-chrome-apps,MobileChromeApps/mobile-chrome-apps,MobileChromeApps/mobile-chrome-apps,chirilo/mobile-chrome-apps