measuring the time it takes to render a tile

Change-Id: I37db170af0e507c99d571b94ff78a1987944290e
releasing the CGDataProvider to prevent possible memory leaks

Change-Id: Ib64f457bd9cc185e979b1a3e9f07fdba93da88d7
release BitmapReadAccess after use to fix 1 mb per render mem leak

Change-Id: I4d9a580132eb9a8d618c1165f962b47be4e80695