Merge "b/2353646 Fix music visualizations to also work with audiotrack...

Merge "b/2353646 Fix music visualizations to also work with audiotrack callbacks, which stagefright uses. This slightly changes the way the data is stored, since before we were relying on the buffers being written always being at least 4K, whereas the callbacks are generally for smaller amounts of data. Now we append all the data to a big circular buffer, then return chunks of that buffer for visualization. When there are multiple things playing at the same time, this will give the wrong result, but (1) that was the case before as well, and (2) will be fixed once we start visualizing the mixer output instead of the mixer inputs."