Convert UtilityProcessHost to bootstrap Mojo Channel using the Shell connection

services/shell/shell.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/shell/shell.h"
 
 #include <stdint.h>
 
 #include <utility>
 
@@ skipping 561 matching lines @@
 
   mojom::ShellResolverPtr resolver_ptr;
   ConnectToInterface(this, identity, CreateCatalogIdentity(), &resolver_ptr);
   mojom::ShellResolver* resolver = resolver_ptr.get();
   identity_to_resolver_[identity] = std::move(resolver_ptr);
   return resolver;
 }
 
 void Shell::TerminateShellConnections() {
   Instance* instance = GetExistingInstance(CreateShellIdentity());
-  DCHECK(instance);
-  OnInstanceError(instance);
+  // The Shell instance may have been destructed as a result of the client
+  // closing its connector.
+  if (instance)
+    OnInstanceError(instance);
 }
 
 void Shell::OnInstanceError(Instance* instance) {
   const Identity identity = instance->identity();
   // Remove the shell.
   auto it = identity_to_instance_.find(identity);
   DCHECK(it != identity_to_instance_.end());
   int id = instance->id();
   identity_to_instance_.erase(it);
   instance_listeners_.ForAllPtrs([this, id](mojom::InstanceListener* listener) {
@@ skipping 195 matching lines @@
   // Now that the instance has a ShellClient, we can connect to it.
   bool connected = instance->ConnectToClient(&params);
   DCHECK(connected);
 }
 
 base::WeakPtr<Shell> Shell::GetWeakPtr() {
   return weak_ptr_factory_.GetWeakPtr();
 }
 
 }  // namespace shell