Enable spare RenderProcessHost to be preinitialized.

content/public/test/mock_render_process_host.cc

Index: content/public/test/mock_render_process_host.cc
diff --git a/content/public/test/mock_render_process_host.cc b/content/public/test/mock_render_process_host.cc
index efabfce444a60371907bca9a41666f0b3fdac22d..c82fac6570b8e5f5d2044500c0ff2e622e345f63 100644
--- a/content/public/test/mock_render_process_host.cc
+++ b/content/public/test/mock_render_process_host.cc
@@ -367,6 +367,10 @@ void MockRenderProcessHost::SetIsUsed() {
   is_unused_ = false;
 }
 
+bool MockRenderProcessHost::HostHasNotBeenUsed() {
+  return IsUnused() && listeners_.IsEmpty() && GetWorkerRefCount() == 0;
+}
+
 void MockRenderProcessHost::FilterURL(bool empty_allowed, GURL* url) {
   RenderProcessHostImpl::FilterURL(this, empty_allowed, url);
 }