Convert UtilityProcessHost to bootstrap Mojo Channel using the Shell connection

services/shell/shell.cc

Index: services/shell/shell.cc
diff --git a/services/shell/shell.cc b/services/shell/shell.cc
index 79763bfa0b3459a65d2015fd0aeed1c2e865ef2a..76f41cb75bb30dffeba7702e87a52b8c8b56d7b6 100644
--- a/services/shell/shell.cc
+++ b/services/shell/shell.cc
@@ -579,8 +579,10 @@ mojom::ShellResolver* Shell::GetResolver(const Identity& identity) {
 
 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) {