Put PrintingUIWebContentsObserver and PrintingMessageFilter into printing namespace.

chrome/browser/printing/print_job_worker.h

Index: chrome/browser/printing/print_job_worker.h
diff --git a/chrome/browser/printing/print_job_worker.h b/chrome/browser/printing/print_job_worker.h
index e3e9a6747014fb4a97fe0bd7c6ae40395f4a3c06..2f6d2371c99181bf7531be021235c7bd2cbf60b1 100644
--- a/chrome/browser/printing/print_job_worker.h
+++ b/chrome/browser/printing/print_job_worker.h
@@ -14,18 +14,17 @@
 #include "printing/printing_context.h"
 #include "printing/print_job_constants.h"
 
-class PrintingUIWebContentsObserver;
-
 namespace base {
 class DictionaryValue;
 }
 
 namespace printing {
 
-class PrintedDocument;
-class PrintedPage;
 class PrintJob;
 class PrintJobWorkerOwner;
+class PrintedDocument;
+class PrintedPage;
+class PrintingUIWebContentsObserver;
 
 // Worker thread code. It manages the PrintingContext, which can be blocking
 // and/or run a message loop. This is the object that generates most