Allow one-copy task tile worker pool to use compressed textures.

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 0849c516bab58e63b183c957eb877e748f85187a..c2bb3e9f37895177bf55f3b2b38dcc4a3e4a7927 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -767,6 +767,13 @@ gfx::Size PictureLayerImpl::CalculateTileSize(
     tile_height = std::min(tile_height, default_tile_height);
   }
 
+  // Ensure that tiles are an even multiple of 4 in size.

[reveman, 2015/12/01 17:27:24]

Unconditionally use MathUtil::UncheckedRoundUp(tile_.., 4)?

Also, can you define something like kTileMinimalAlignment with a comment
explaining why we need it instead of just using the magic value of 4?

[christiank, 2015/12/02 16:18:14]

Done.

+  if (tile_width % 4 != 0 || tile_height % 4 != 0) {
+    // Round the size up to the nearest multiple of four.
+    tile_width = 4 * std::ceil(static_cast<float>(tile_width) / 4);
+    tile_height = 4 * std::ceil(static_cast<float>(tile_height) / 4);
+  }
+
   // Under no circumstance should we be larger than the max texture size.
   tile_width = std::min(tile_width, max_texture_size);
   tile_height = std::min(tile_height, max_texture_size);