A snapshot of what a DocumentSession is doing and holding.
public SessionStatistics(int PendingOperations, long PixelBytes, long TilesPresented, long TilesCancelled)
Page loads, display-list builds and tile renders started and not finished.
Bytes of pooled tile pixels the session holds right now (0 once every render has finished).
Tiles handed to a surface since the session opened.
Tile renders cancelled (by their token or by closing the session) since the session opened.
Spec #33 story 54; the tile scheduler's memory budget (viewer capability 13) reads PixelBytes.