cache contains 0 tracks on first load

[simon-weber]

This is a weird one. Here's what happened:

• signed into chrome for the first time on a new linux computer
• opened google music, extension initialized as expected and synced extension state properly (notable, TypeError: Cannot read property 'getName' of undefined #41 did not happen)
• autoplaylists were cleared on the first sync
• testing a new autoplaylist showed that the track cache contained 0 items
• once a song finished playing, the track cache contained just it
• reloading the extension then the page fixed the problem

My best guess is that the indexedb contained 0 tracks on the first load, since the diff update should work to pull the entire library. This makes sense, since google's client wouldn't have had a chance to pull down the library yet.

I'm not sure how to detect this since I didn't get a good look at the idb before reloading the page (oops). At very least, it ought to be possible to test this hypothesis by blowing away all cached data for google music, then reloading the page.