GameBench: curCell doesn't need to be extra state.

We're using a static curCell to loop around the atlas.  We can just use i.

Noticed this when TSAN complained about it.  Parallel invocations of the
game bench were stomping on each other's curCell.

BUG=skia:1792
R=robertphillips@google.com, mtklein@google.com

Author: mtklein@chromium.org

Review URL: https://codereview.chromium.org/270273006

git-svn-id: http://skia.googlecode.com/svn/trunk@14617 2bbb7eff-a529-9590-31e7-b0007b416f81

bench/GameBench.cpp

@@ -190,9 +190,8 @@ protected:
 
             canvas->concat(mat);
             if (fUseAtlas) {
-                static int curCell = 0;
+                const int curCell = i % (kNumAtlasedX * kNumAtlasedY);
                 SkIRect src = fAtlasRects[curCell % (kNumAtlasedX)][curCell / (kNumAtlasedX)];
-                curCell = (curCell + 1) % (kNumAtlasedX*kNumAtlasedY);
 
                 if (fUseDrawVertices) {
                     SkPoint uvs[4] = {