Add src/printing to the GN build.

BUG=
[email protected]

Review URL: https://codereview.chromium.org/311603003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@274865 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/BUILD.gn b/BUILD.gn
index 384834a..29013c3 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -48,6 +48,7 @@
     "//mojo",
     "//net",
     "//ppapi:ppapi_c",
+    "//printing",
     #"//sandbox",
     "//sdch",
     "//skia",