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

content/test/render_view_fake_resources_test.cc

Index: content/test/render_view_fake_resources_test.cc
===================================================================
--- content/test/render_view_fake_resources_test.cc	(revision 118690)
+++ content/test/render_view_fake_resources_test.cc	(working copy)
@@ -67,8 +67,9 @@
 
   webkit_glue::SetJavaScriptFlags("--expose-gc");
   mock_process_.reset(new MockRenderProcess);
+  // The RenderThreadImpl will register itself as the main thread for the
+  // current process.
   render_thread_ = new RenderThreadImpl(kThreadName);
-  mock_process_->set_main_thread(render_thread_);
 #if defined(OS_MACOSX)
   InitWebCoreSystemInterface();
 #endif