Make Service own ServiceContext.

mash/webtest/webtest.h

Index: mash/webtest/webtest.h
diff --git a/mash/webtest/webtest.h b/mash/webtest/webtest.h
index f1897b0e2de0d9c5a669ea33374dd9cf4c48a75b..344d1cf56e51aad9a231610ad5b5902ae1f2e953 100644
--- a/mash/webtest/webtest.h
+++ b/mash/webtest/webtest.h
@@ -35,9 +35,7 @@ class Webtest
 
  private:
   // shell::Service:
-  void OnStart(shell::Connector* connector,
-               const shell::Identity& identity,
-               uint32_t id) override;
+  void OnStart(const shell::Identity& identity) override;
   bool OnConnect(shell::Connection* connection) override;
 
   // mojom::Launchable:
@@ -47,7 +45,6 @@ class Webtest
   void Create(const shell::Identity& remote_identity,
               mojom::LaunchableRequest request) override;
 
-  shell::Connector* connector_ = nullptr;
   mojo::BindingSet<mojom::Launchable> bindings_;
   std::vector<views::Widget*> windows_;