private void onSourceRead() {
        // guaranteed notify listeners after source read and cache completed
        percentsAvailable = 100;
        onCachePercentsAvailableChanged(percentsAvailable);
    }
Proxy for {@link Source} with caching support ({@link Cache}).
<p/>
Can be used only for sources with persistent data (that doesn't change with time).
Method {@link #read(byte[], long, int)} will be blocked while fetching data from source.
Useful for streaming something with caching e.g. streaming video/audio etc.

@author Alexey Danilov (danikula@gmail.com).
dkplayer-videocache/src/main/java/com/danikula/videocache/ProxyCache.java