Set up content in-process main threads via factory

content/public/test/content_test_suite_base.cc

Index: content/public/test/content_test_suite_base.cc
diff --git a/content/public/test/content_test_suite_base.cc b/content/public/test/content_test_suite_base.cc
index 5bf5b5eded1cb0668a5476cad4086ae013d39fe7..f59c8c2a58807368699041a1998b444529d7e484 100644
--- a/content/public/test/content_test_suite_base.cc
+++ b/content/public/test/content_test_suite_base.cc
@@ -10,9 +10,15 @@
 #include "base/test/test_suite.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "content/browser/browser_thread_impl.h"
+#include "content/browser/gpu/gpu_process_host.h"
 #include "content/common/url_schemes.h"
+#include "content/gpu/gpu_main_thread.h"
+#include "content/public/browser/render_process_host.h"
+#include "content/public/browser/utility_process_host.h"
 #include "content/public/common/content_client.h"
 #include "content/public/common/content_paths.h"
+#include "content/renderer/renderer_main_thread.h"
+#include "content/utility/utility_main_thread.h"
 #include "media/base/media.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/base/ui_base_paths.h"
@@ -60,6 +66,11 @@ void ContentTestSuiteBase::Initialize() {
   ui::shell_dialogs::RegisterJni(env);
 #endif
 
+  UtilityProcessHost::RegisterUtilityMainThreadFactory(CreateUtilityMainThread);
+  RenderProcessHost::RegisterRendererMainThreadFactory(
+      CreateRendererMainThread);
+  GpuProcessHost::RegisterGpuMainThreadFactory(CreateGpuMainThread);
+
   if (external_libraries_enabled_)
     media::InitializeMediaLibraryForTesting();