Remove old session history logic.

content/browser/frame_host/render_frame_host_impl.cc

Index: content/browser/frame_host/render_frame_host_impl.cc
diff --git a/content/browser/frame_host/render_frame_host_impl.cc b/content/browser/frame_host/render_frame_host_impl.cc
index 5c8413f8f5ef01d50019032090e308a717b713ce..d2ff0257f52f993b11c6983ac062c45e299e7f68 100644
--- a/content/browser/frame_host/render_frame_host_impl.cc
+++ b/content/browser/frame_host/render_frame_host_impl.cc
@@ -1067,8 +1067,6 @@ void RenderFrameHostImpl::OnOpenURL(const FrameHostMsg_OpenURL_Params& params) {
   GetProcess()->FilterURL(false, &validated_url);
 
   if (params.is_history_navigation_in_new_child) {
-    DCHECK(SiteIsolationPolicy::UseSubframeNavigationEntries());
-
     // Try to find a FrameNavigationEntry that matches this frame instead, based
     // on the frame's unique name.  If this can't be found, fall back to the
     // default params using RequestOpenURL below.