Change ChildProcess::set_main_thread registration to occur inside the RenderThreadImpl::Init method.

content/renderer/renderer_main.cc

Index: content/renderer/renderer_main.cc
===================================================================
--- content/renderer/renderer_main.cc	(revision 119665)
+++ content/renderer/renderer_main.cc	(working copy)
@@ -215,7 +215,7 @@
     // TODO(markus): Check if it is OK to unconditionally move this
     // instruction down.
     RenderProcessImpl render_process;
-    render_process.set_main_thread(new RenderThreadImpl());
+    new RenderThreadImpl();
 #endif
     bool run_loop = true;
     if (!no_sandbox) {
@@ -225,7 +225,7 @@
     }
 #if defined(OS_POSIX) && !defined(OS_MACOSX)
     RenderProcessImpl render_process;
-    render_process.set_main_thread(new RenderThreadImpl());
+    new RenderThreadImpl();
 #endif
 
     platform.RunSandboxTests();