Put PrintingUIWebContentsObserver and PrintingMessageFilter into printing namespace.

chrome/browser/printing/printing_ui_web_contents_observer.cc

Index: chrome/browser/printing/printing_ui_web_contents_observer.cc
diff --git a/chrome/browser/printing/printing_ui_web_contents_observer.cc b/chrome/browser/printing/printing_ui_web_contents_observer.cc
index 541e93392747573e7d503da088789babc2554765..71932c2f685881859c0fecd78ea08aebe5113d9e 100644
--- a/chrome/browser/printing/printing_ui_web_contents_observer.cc
+++ b/chrome/browser/printing/printing_ui_web_contents_observer.cc
@@ -7,6 +7,8 @@
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/web_contents.h"
 
+namespace printing {
+
 PrintingUIWebContentsObserver::PrintingUIWebContentsObserver(
     content::WebContents* web_contents)
     : content::WebContentsObserver(web_contents) {
@@ -21,3 +23,5 @@ gfx::NativeView PrintingUIWebContentsObserver::GetParentView() {
   DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
   return web_contents() ? web_contents()->GetNativeView() : NULL;
 }
+
+}  // namespace printing