Swap iteration order in TileGrid::insert().

Was looking at performance here (it's the record hotspot) and noticed we
iterate through the grid out of order.  This is a tiny little thing, but it's
probably orthogonal to any other performance improvements we'll make in here.

BUG=skia:
R=robertphillips@google.com, mtklein@google.com

Author: mtklein@chromium.org

Review URL: https://codereview.chromium.org/598933004
1 file changed