Round GPU tiles to multiple of 64 to work around CA scaling issues

cc/layers/picture_layer_impl.cc

Index: cc/layers/picture_layer_impl.cc
diff --git a/cc/layers/picture_layer_impl.cc b/cc/layers/picture_layer_impl.cc
index 43ea41176a73e8becafcb1d0d8c86c9180db9800..ba56562ecaafcd78320ab85e07f3dd1c06c8f6c1 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -767,6 +767,13 @@ gfx::Size PictureLayerImpl::CalculateTileSize(
     default_tile_width += 2 * PictureLayerTiling::kBorderTexels;
     default_tile_height += 2 * PictureLayerTiling::kBorderTexels;
 
+    // Round GPU default tile sizes to a multiple of kTileRoundUp. This
+    // helps prevent rounding errors in our CA path. crbug.com/632274
+    default_tile_width =
+        MathUtil::UncheckedRoundUp(default_tile_width, kTileRoundUp);
+    default_tile_height =
+        MathUtil::UncheckedRoundUp(default_tile_height, kTileRoundUp);
+
     default_tile_height =
         std::max(default_tile_height, kMinHeightForGpuRasteredTile);
   } else {