Add PDF compositor service

Currently, the service converts one or multiple pages encapsulated in a
SkMultiPictureDocument to a PDF file. It runs in a sandboxed utility process.

This allows Chromium to move PDF generation code into a separate
process, and eventually can support compositing content generated from
multiple processes.

BUG=455764

Review-Url: https://codereview.chromium.org/2832633002
Cr-Commit-Position: refs/heads/master@{#473644}
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index 7df13cf0..c637153b 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -2581,6 +2581,7 @@
     ]
     deps += [
       "//components/printing/browser",
+      "//components/printing/service/public/interfaces",
       "//printing",
     ]