Set up content in-process main threads via factory

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 8908a1035db4021ccd27c4978833dfcaf3908274..32345b728004ebb1ee017b1268b425e65143ed2d 100644
--- a/content/browser/gpu/gpu_process_host.h
+++ b/content/browser/gpu/gpu_process_host.h
@@ -44,6 +44,8 @@ class GpuMainThread;
 class RenderWidgetHostViewFrameSubscriber;
 class ShaderDiskCache;
 
+typedef base::Thread* (*GpuMainThreadFactoryFunction)(const std::string& id);
+
 class GpuProcessHost : public BrowserChildProcessHostDelegate,
                        public IPC::Sender,
                        public base::NonThreadSafe {
@@ -82,6 +84,9 @@ class GpuProcessHost : public BrowserChildProcessHostDelegate,
                                       CauseForGpuLaunch cause,
                                       IPC::Message* message);
 
+  CONTENT_EXPORT static void RegisterGpuMainThreadFactory(
+      GpuMainThreadFactoryFunction create);
+
   // Get the GPU process host for the GPU process with the given ID. Returns
   // null if the process no longer exists.
   static GpuProcessHost* FromID(int host_id);
@@ -214,9 +219,7 @@ class GpuProcessHost : public BrowserChildProcessHostDelegate,
   bool swiftshader_rendering_;
   GpuProcessKind kind_;
 
-#if !defined(CHROME_MULTIPLE_DLL)
-  scoped_ptr<GpuMainThread> in_process_gpu_thread_;
-#endif
+  scoped_ptr<base::Thread> in_process_gpu_thread_;
 
   // Whether we actually launched a GPU process.
   bool process_launched_;