Check BrowsingInstance before swapping prerenders.

content/browser/site_instance_impl.cc

Index: content/browser/site_instance_impl.cc
diff --git a/content/browser/site_instance_impl.cc b/content/browser/site_instance_impl.cc
index 9bb1e755d8f79cba7ed92396667d27d60b33f799..b6e6918c0a48d755b0ae631270858c440afd3cb0 100644
--- a/content/browser/site_instance_impl.cc
+++ b/content/browser/site_instance_impl.cc
@@ -182,6 +182,10 @@ bool SiteInstanceImpl::IsRelatedSiteInstance(const SiteInstance* instance) {
                                          instance)->browsing_instance_.get();
 }
 
+size_t SiteInstanceImpl::GetRelatedActiveContentsCount() {
+  return browsing_instance_->active_contents_count();
+}
+
 bool SiteInstanceImpl::HasWrongProcessForURL(const GURL& url) {
   // Having no process isn't a problem, since we'll assign it correctly.
   // Note that HasProcess() may return true if process_ is null, in
@@ -203,6 +207,14 @@ bool SiteInstanceImpl::HasWrongProcessForURL(const GURL& url) {
       GetProcess(), browsing_instance_->browser_context(), site_url);
 }
 
+void SiteInstanceImpl::IncrementRelatedActiveContentsCount() {
+  browsing_instance_->increment_active_contents_count();
+}
+
+void SiteInstanceImpl::DecrementRelatedActiveContentsCount() {
+  browsing_instance_->decrement_active_contents_count();
+}
+
 void SiteInstanceImpl::set_render_process_host_factory(
     const RenderProcessHostFactory* rph_factory) {
   g_render_process_host_factory_ = rph_factory;