Plug memory leak that happens when reusing display lists

Bug #7195815

We did not reclaim resources when reusing an existing DisplayList to
record a new empty list of commands. This would lead to various memory
leaks: bitmaps, paints, paths, matrices, etc.

This is not a common case but some apps run into this situation,
such as Launcher.

Change-Id: I2eb14ac86a212123f8edbe42b70a7c1c51fa4145