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

content/browser/gpu/gpu_process_host.h

Index: content/browser/gpu/gpu_process_host.h
diff --git a/content/browser/gpu/gpu_process_host.h b/content/browser/gpu/gpu_process_host.h
index 1ed58728583cdaacaeb41efcc657d7b53a124a0b..6226e0535d30adb414e3185df3fa6cb6e7f07205 100644
--- a/content/browser/gpu/gpu_process_host.h
+++ b/content/browser/gpu/gpu_process_host.h
@@ -56,10 +56,6 @@ class InterfaceProvider;
 
 namespace content {
 class BrowserChildProcessHostImpl;
-class InProcessChildThreadParams;
-
-typedef base::Thread* (*GpuMainThreadFactoryFunction)(
-    const InProcessChildThreadParams&, const gpu::GpuPreferences&);
 
 class GpuProcessHost : public BrowserChildProcessHostDelegate,
                        public IPC::Sender,
@@ -111,9 +107,6 @@ class GpuProcessHost : public BrowserChildProcessHostDelegate,
                                       bool force_create,
                                       IPC::Message* message);
 
-  CONTENT_EXPORT static void RegisterGpuMainThreadFactory(
-      GpuMainThreadFactoryFunction create);
-
   service_manager::InterfaceProvider* GetRemoteInterfaces();
 
   // Get the GPU process host for the GPU process with the given ID. Returns