After bug 831265 landed, users are able to view all songs by tapping the "songs" tab. Currently we use MediaDB.enumerate() to show all songs, but it takes long time to finish displaying all song elements on the ui, and will cause the scrolling in the songs list feels slow. As Daivd suggested, we can probably use a model where we query all the songs from the db once at startup, and keep the list in memory so that we don't have to do any other db operations after starting.

Bug 901421 has added one new method(MediaDB.advancedEnumerate()) and plus the pattern that draw the first few pages, then draw the rest after the user scrolls the list, it should solved this issue because, what bug 901421 has done is reducing the updates on ui(appending children to the DOM and causes repaint) which is the root cause that slows down the scrolling.