When cloning picture, use a bitmap heap to avoid flattening bitmaps.

When cloning a picture, the paints are reflattened. Use a bitmap
heap so the bitmaps do not get unnecessarily get flattened as well.

For br.337, this speeds up bench_pictures timing the clone
operation (not yet checked in, but currently timing making five
clones) from around 180 ms to around 24ms.

Review URL: https://codereview.appspot.com/6903063

git-svn-id: http://skia.googlecode.com/svn/trunk@6740 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed