Rename shell namespace to service_manager

mash/webtest/main.cc

Index: mash/webtest/main.cc
diff --git a/mash/webtest/main.cc b/mash/webtest/main.cc
index d2b859167e4478bc8eb682bc6307964d13c9d64a..470d2385513b710573e615b09eaada2337397306 100644
--- a/mash/webtest/main.cc
+++ b/mash/webtest/main.cc
@@ -7,6 +7,6 @@
 #include "services/service_manager/public/cpp/service_runner.h"
 
 MojoResult ServiceMain(MojoHandle service_request_handle) {
-  shell::ServiceRunner runner(new mash::webtest::Webtest);
+  service_manager::ServiceRunner runner(new mash::webtest::Webtest);
   return runner.Run(service_request_handle);
 }