Merge "Updating code sample for "displaying bitmaps efficiently" training class. Changes:  -Use updated versions of ImageWorker & ImageCache from I/O 2012 app  -Use copied DiskLruCache from system (rather than custom)  -Use copied AsyncTask from system (to keep behavior consistent)  -Ensure no strict mode violations or lint errors  -Other misc bug fixes  -Move single-use static methods in Utils to corresponding class" into jb-dev