Experimentally isolate OpenItemViaShell in a utility process.

content/public/browser/utility_process_host.h

Index: content/public/browser/utility_process_host.h
diff --git a/content/public/browser/utility_process_host.h b/content/public/browser/utility_process_host.h
index 756d50f1d1e980d9283ed663b8648989286db58a..51a89fab1003135a4486b80efbc06a930b3d1b1d 100644
--- a/content/public/browser/utility_process_host.h
+++ b/content/public/browser/utility_process_host.h
@@ -34,7 +34,10 @@ struct ChildProcessData;
 class UtilityProcessHost : public IPC::Sender,
                            public base::SupportsWeakPtr<UtilityProcessHost> {
  public:
-  // Used to create a utility process.
+  // Used to create a utility process. |client| is optional. If supplied it will
+  // be notified of incoming messages from the utility process.
+  // |client_task_runner| is required if |client| is supplied and is the task
+  // runner upon which |client| will be invoked.
   CONTENT_EXPORT static UtilityProcessHost* Create(
       UtilityProcessHostClient* client,
       base::SequencedTaskRunner* client_task_runner);