Add gpu_main_thread_factory.h to expose less of content's guts.

content/app/content_main_runner.cc

Index: content/app/content_main_runner.cc
diff --git a/content/app/content_main_runner.cc b/content/app/content_main_runner.cc
index ee6ab17a0dc24ac400302dd074a0b2cdae168332..129396c4e5db3552226f5996c3e85080a17b4c1d 100644
--- a/content/app/content_main_runner.cc
+++ b/content/app/content_main_runner.cc
@@ -113,7 +113,7 @@
 #endif
 
 #if !defined(CHROME_MULTIPLE_DLL_BROWSER) && !defined(CHROME_MULTIPLE_DLL_CHILD)
-#include "content/browser/gpu/gpu_process_host.h"
+#include "content/browser/gpu/gpu_main_thread_factory.h"
 #endif
 
 #if BUILDFLAG(ENABLE_PEPPER_CDMS)
@@ -376,8 +376,7 @@ static void RegisterMainThreadFactories() {
       CreateInProcessUtilityThread);
   RenderProcessHostImpl::RegisterRendererMainThreadFactory(
       CreateInProcessRendererThread);
-  GpuProcessHost::RegisterGpuMainThreadFactory(
-      CreateInProcessGpuThread);
+  content::RegisterGpuMainThreadFactory(CreateInProcessGpuThread);
 #else
   base::CommandLine& command_line = *base::CommandLine::ForCurrentProcess();
   if (command_line.HasSwitch(switches::kSingleProcess)) {