Cleanup: Use base namespace in printing/.

printing/backend/print_backend.cc

Index: printing/backend/print_backend.cc
===================================================================
--- printing/backend/print_backend.cc	(revision 224775)
+++ printing/backend/print_backend.cc	(working copy)
@@ -38,12 +38,13 @@
 
 PrintBackend::~PrintBackend() {}
 
-string16 PrintBackend::SimplifyDocumentTitle(const string16& title) {
-  string16 no_controls(title);
+base::string16 PrintBackend::SimplifyDocumentTitle(
+    const base::string16& title) {
+  base::string16 no_controls(title);
   no_controls.erase(
     std::remove_if(no_controls.begin(), no_controls.end(), &u_iscntrl),
     no_controls.end());
-  string16 result;
+  base::string16 result;
   gfx::ElideString(no_controls, kMaxDocumentTitleLength, &result);
   return result;
 }