Get rid of KeepAlive. Quit shell when all urls run directly by Context are closed.

mojo/shell/run.cc

Index: mojo/shell/run.cc
diff --git a/mojo/shell/run.cc b/mojo/shell/run.cc
index 733b19132de2188956258547e69529f803e13543..3cdb7043f4a9d8b24029cdbc96467bf3c8cd6374 100644
--- a/mojo/shell/run.cc
+++ b/mojo/shell/run.cc
@@ -7,7 +7,6 @@
 #include "base/logging.h"
 #include "mojo/application_manager/application_manager.h"
 #include "mojo/shell/context.h"
-#include "mojo/shell/keep_alive.h"
 
 namespace mojo {
 namespace shell {
@@ -22,8 +21,6 @@ class StubServiceProvider : public InterfaceImpl<ServiceProvider> {
 
 
 void Run(Context* context, const std::vector<GURL>& app_urls) {
-  KeepAlive keep_alive(context);
-
   if (app_urls.empty()) {
     LOG(ERROR) << "No app path specified";
     return;