Music: add cache for getArtworkFromFile() to improve performance

getArtworkFromFile() is called many times to get the art of the same song
when play a song, and it has IO action, add cache for the method to improve
performance.

Change-Id: I2b0616291bd0154409d4ef2a465ab11b537a5eb9
CRs-Fixed: 1022935
1 file changed