Mandoline: Introduce ApplicationConnection::CloseConnection

mojo/application/public/cpp/application_connection.h

Index: mojo/application/public/cpp/application_connection.h
diff --git a/mojo/application/public/cpp/application_connection.h b/mojo/application/public/cpp/application_connection.h
index ff900d3668c7522e9fae35938adf5eded7b58167..4937fbfa57799405a3fd9325d2c94e87f7fe9a19 100644
--- a/mojo/application/public/cpp/application_connection.h
+++ b/mojo/application/public/cpp/application_connection.h
@@ -40,10 +40,16 @@ class ServiceConnector;
 //
 // Just as with InterfaceFactory, ServiceConnector must outlive
 // ApplicationConnection.
+//
+// An ApplicationConnection's lifetime is managed by an ApplicationImpl. To
+// close a connection, call CloseConnection which will destroy this object.
 class ApplicationConnection {
  public:
   virtual ~ApplicationConnection();

[sky, 2015/06/29 16:56:02]

Can the destructor be made protected to prevent accidental usage? Alternatively
can you make it so deleting the connection closes the connection?

[Fady Samuel, 2015/06/29 20:32:36]

I took the following approach.

1. I made ~ApplicationConnection and ~ServiceRegistry protected.
2. I made CloseConnection to be non-virtual.
3. I introduced a protected pure virtual OnCloseConnection() that is overridden
by ServiceRegistry.
4. I introduced a flag connection_closed_ in ApplicationConnection that becomes
true when CloseConnection is called. This both prevents double deletes and
ensures that only CloseConnection can actually destroy the object.
5. I added a DCHECK in ~ApplicationConnection to verify that the
connection_closed_ flag is set.

 
+  // Closes the connection.
+  virtual void CloseConnection() = 0;
+
   // See class description for details.
   virtual void SetServiceConnector(ServiceConnector* connector) = 0;