Extract a Connector interface from Shell that can be cloned & passed to other threads

mojo/shell/public/cpp/lib/application_test_base.cc

Index: mojo/shell/public/cpp/lib/application_test_base.cc
diff --git a/mojo/shell/public/cpp/lib/application_test_base.cc b/mojo/shell/public/cpp/lib/application_test_base.cc
index 49bb65ea7d4a54a7eb7331c101cf40451327f2e4..da56dbb4aa6c6d55b65ad54183c539aeb1c30f41 100644
--- a/mojo/shell/public/cpp/lib/application_test_base.cc
+++ b/mojo/shell/public/cpp/lib/application_test_base.cc
@@ -20,8 +20,8 @@ namespace test {
 namespace {
 // Share the application URL with multiple application tests.
 String g_url;
-uint32_t g_id = shell::mojom::Shell::kInvalidApplicationID;
-uint32_t g_user_id = shell::mojom::Shell::kUserRoot;
+uint32_t g_id = shell::mojom::Connector::kInvalidApplicationID;
+uint32_t g_user_id = shell::mojom::Connector::kUserRoot;
 
 // ShellClient request handle passed from the shell in MojoMain, stored in
 // between SetUp()/TearDown() so we can (re-)intialize new ShellConnections.