Mojo: Make overriding OnConnectionError optional

mojo/examples/launcher/launcher.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <stdio.h>
 #include <string>
 
 #include "base/at_exit.h"
 #include "base/command_line.h"
 #include "base/files/file_path.h"
@@ skipping 188 matching lines @@
     gfx::Screen::SetScreenInstance(gfx::SCREEN_TYPE_NATIVE, screen_.get());
 
     NativeViewportPtr viewport;
     app_->ConnectTo("mojo:mojo_native_viewport_service", &viewport);
 
     window_tree_host_.reset(new WindowTreeHostMojo(
         viewport.Pass(), gfx::Rect(50, 50, 450, 60),
         base::Bind(&LauncherImpl::HostContextCreated, base::Unretained(this))));
   }
 
-  // Overridden from InterfaceImpl:
-  virtual void OnConnectionError() OVERRIDE {}
-
  private:
   // Overridden from Launcher:
   virtual void Show() OVERRIDE {
     if (!window_tree_host_.get()) {
       pending_show_ = true;
       return;
     }
     window_tree_host_->Show();
   }
   virtual void Hide() OVERRIDE {
@@ skipping 65 matching lines @@
   //             MessageLoop is not of TYPE_UI. I think we need a way to build
   //             Aura that doesn't define platform-specific stuff.
   aura::Env::CreateInstance(true);
 
   mojo::Application app(shell_handle);
   app.AddService<mojo::examples::LauncherImpl>(&app);
 
   loop.Run();
   return MOJO_RESULT_OK;
 }