Change GPU Tile rounding to 32

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 ba56562ecaafcd78320ab85e07f3dd1c06c8f6c1..d48a6c2b0c5fd2b6f609781afc309937950da5be 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -52,6 +52,10 @@ const int kMinHeightForGpuRasteredTile = 256;
 // of using the same tile size.
 const int kTileRoundUp = 64;
 
+// Round GPU default tile sizes to a multiple of 32. This helps prevent
+// rounding errors during compositing.
+const int kGpuDefaultTileRoundUp = 32;
+
 // For performance reasons and to support compressed tile textures, tile
 // width and height should be an even multiple of 4 in size.
 const int kTileMinimalAlignment = 4;
@@ -767,12 +771,12 @@ 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
+    // Round GPU default tile sizes to a multiple of kGpuDefaultTileAlignment.
+    // This helps prevent rounding errors in our CA path. crbug.com/632274
     default_tile_width =
-        MathUtil::UncheckedRoundUp(default_tile_width, kTileRoundUp);
+        MathUtil::UncheckedRoundUp(default_tile_width, kGpuDefaultTileRoundUp);
     default_tile_height =
-        MathUtil::UncheckedRoundUp(default_tile_height, kTileRoundUp);
+        MathUtil::UncheckedRoundUp(default_tile_height, kGpuDefaultTileRoundUp);
 
     default_tile_height =
         std::max(default_tile_height, kMinHeightForGpuRasteredTile);