Cache gpu suitability in DisplayItemList, remove SetUnsuitable...ForTesting

cc/playback/picture_pile.cc

Index: cc/playback/picture_pile.cc
diff --git a/cc/playback/picture_pile.cc b/cc/playback/picture_pile.cc
index 1351ac6a98afe418bfa22abc0e1e7596a233aa72..9306cfd1d55661a95b5ba1647d2e78c756b9b1c8 100644
--- a/cc/playback/picture_pile.cc
+++ b/cc/playback/picture_pile.cc
@@ -612,10 +612,6 @@ void PicturePile::SetTileGridSize(const gfx::Size& tile_grid_size) {
   tile_grid_size_ = tile_grid_size;
 }
 
-void PicturePile::SetUnsuitableForGpuRasterizationForTesting() {
-  is_suitable_for_gpu_rasterization_ = false;
-}
-
 bool PicturePile::CanRasterSlowTileCheck(const gfx::Rect& layer_rect) const {
   bool include_borders = false;
   for (TilingData::Iterator tile_iter(&tiling_, layer_rect, include_borders);