Add PDF compositor service

components/printing/service/public/interfaces/BUILD.gn

Index: components/printing/service/public/interfaces/BUILD.gn
diff --git a/components/printing/service/public/interfaces/BUILD.gn b/components/printing/service/public/interfaces/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..1efdb19418da26c6a1858961fc82dc37d756a0ba
--- /dev/null
+++ b/components/printing/service/public/interfaces/BUILD.gn
@@ -0,0 +1,11 @@
+# Copyright 2017 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import("//mojo/public/tools/bindings/mojom.gni")
+
+mojom("interfaces") {
+  sources = [
+    "pdf_compositor.mojom",
+  ]
+}