//pdf contains the PDF plugin, its Blink-based replacement, as well as PDF
utility functions that leverage PDFium. It can use low-level components that
live below the content layer, as well as other foundational code like
//printing. It should not use //content or anything in //components that
lives above the content layer. Code that lives above the content layer should
live in //components/pdf, or in the embedder. All the code here should run in
sandboxed child processes.