Put PrintingUIWebContentsObserver and PrintingMessageFilter into printing namespace.

chrome/browser/printing/print_job_worker.cc

Index: chrome/browser/printing/print_job_worker.cc
diff --git a/chrome/browser/printing/print_job_worker.cc b/chrome/browser/printing/print_job_worker.cc
index 4f468cff3998571cc28623fdb12222502b0acbc8..e7f4d329443ce21992df9c9e48fdc43e45df2f57 100644
--- a/chrome/browser/printing/print_job_worker.cc
+++ b/chrome/browser/printing/print_job_worker.cc
@@ -25,6 +25,8 @@
 
 using content::BrowserThread;
 
+namespace printing {
+
 namespace {
 
 // Helper function to ensure |owner| is valid until at least |callback| returns.
@@ -35,8 +37,6 @@ void HoldRefCallback(const scoped_refptr<printing::PrintJobWorkerOwner>& owner,
 
 }  // namespace
 
-namespace printing {
-
 void NotificationCallback(PrintJobWorkerOwner* print_job,
                           JobEventDetails::Type detail_type,
                           PrintedDocument* document,