Enable spare RenderProcessHost to be preinitialized.

content/browser/frame_host/render_frame_host_manager.cc

Index: content/browser/frame_host/render_frame_host_manager.cc
diff --git a/content/browser/frame_host/render_frame_host_manager.cc b/content/browser/frame_host/render_frame_host_manager.cc
index f66dac33cdaf72794e6c0aaaa5bf9e34212b7aac..af7ba906a7c3f8bf037204bf2b2fd1ef813b9836 100644
--- a/content/browser/frame_host/render_frame_host_manager.cc
+++ b/content/browser/frame_host/render_frame_host_manager.cc
@@ -1200,6 +1200,12 @@ RenderFrameHostManager::GetSiteInstanceForNavigation(
   if (force_swap)
     CHECK_NE(new_instance, current_instance);
 
+  if (new_instance == current_instance) {
+    // If we're navigating to the same site instance, we won't need to use any
+    // spare RenderProcessHost.
+    RenderProcessHostImpl::CleanupSpareRenderProcessHost();
+  }
+
   // Double-check that the new SiteInstance is associated with the right
   // BrowserContext.
   DCHECK_EQ(new_instance->GetBrowserContext(), browser_context);