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
diff --git a/src/core/SkTileGrid.cpp b/src/core/SkTileGrid.cpp
index 84dc949..2eea6db 100644
--- a/src/core/SkTileGrid.cpp
+++ b/src/core/SkTileGrid.cpp
@@ -52,8 +52,8 @@
                                   fYTiles - 1));
 
     Entry entry = { fCount++, data };
-    for (int x = minX; x <= maxX; x++) {
-        for (int y = minY; y <= maxY; y++) {
+    for (int y = minY; y <= maxY; y++) {
+        for (int x = minX; x <= maxX; x++) {
             fTiles[y * fXTiles + x].push(entry);
         }
     }