Fix crash in ViewManager: fail gracefully when no ServiceProvider is

services/view_manager/view_manager_app.cc

 // Copyright 2014 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 "services/view_manager/view_manager_app.h"
 
 #include "mojo/application/application_runner_chromium.h"
 #include "mojo/common/tracing_impl.h"
 #include "mojo/public/c/system/main.h"
 #include "mojo/public/cpp/application/application_connection.h"
@@ skipping 27 matching lines @@
   if (connection_manager_.get()) {
     VLOG(1) << "ViewManager allows only one window manager connection.";
     return false;
   }
   wm_app_connection_ = connection;
   // |connection| originates from the WindowManager. Let it connect directly
   // to the ViewManager and WindowManagerInternalClient.
   connection->AddService<ViewManagerService>(this);
   connection->AddService<WindowManagerInternalClient>(this);
   connection->ConnectToService(&wm_internal_);
+  // If no ServiceProvider has been sent, refuse the connection.

[sky, 2015/03/06 18:25:28]

This doesn't make sense. It is expected that the first connection is the window
manager and further that we can get WindowManagerInternal from it.

+  if (!wm_internal_)
+    return false;
   wm_internal_.set_error_handler(this);
 
   scoped_ptr<DefaultDisplayManager> display_manager(new DefaultDisplayManager(
       app_impl_, connection,
       base::Bind(&ViewManagerApp::OnLostConnectionToWindowManager,
                  base::Unretained(this))));
   connection_manager_.reset(
       new ConnectionManager(this, display_manager.Pass(), wm_internal_.get()));
   return true;
 }
@@ skipping 67 matching lines @@
   wm_internal_client_binding_->set_error_handler(this);
   wm_internal_->SetViewManagerClient(
       wm_internal_client_request_.PassMessagePipe());
 }
 
 void ViewManagerApp::OnConnectionError() {
   ApplicationImpl::Terminate();
 }
 
 }  // namespace view_manager