Set up content in-process main threads via factory

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 4c7e192627602dcf65390da51d2abb1eeaba3018..d85df1e887def5f9884d326d6d570b30f02a47c4 100644
--- a/content/public/browser/utility_process_host.h
+++ b/content/public/browser/utility_process_host.h
@@ -6,6 +6,7 @@
 #define CONTENT_PUBLIC_BROWSER_UTILITY_PROCESS_HOST_H_
 
 #include "base/process/launch.h"
+#include "base/threading/thread.h"
 #include "content/common/content_export.h"
 #include "ipc/ipc_sender.h"
 
@@ -18,6 +19,9 @@ namespace content {
 class UtilityProcessHostClient;
 struct ChildProcessData;
 
+typedef base::Thread* (*UtilityMainThreadFactoryFunction)(
+    const std::string& id);
+
 // This class acts as the browser-side host to a utility child process.  A
 // utility process is a short-lived process that is created to run a specific
 // task.  This class lives solely on the IO thread.
@@ -66,6 +70,9 @@ class UtilityProcessHost : public IPC::Sender,
 #if defined(OS_POSIX)
   virtual void SetEnv(const base::EnvironmentVector& env) = 0;
 #endif
+
+  CONTENT_EXPORT static void RegisterUtilityMainThreadFactory(
+      UtilityMainThreadFactoryFunction create);
 };
 
 };  // namespace content