Remove old session history logic.

content/common/site_isolation_policy.h

Index: content/common/site_isolation_policy.h
diff --git a/content/common/site_isolation_policy.h b/content/common/site_isolation_policy.h
index c6d6e6132aad0d365a265454db8626268b5944a7..3e70f6450bd01a111444c9f0c5f5ad651123f1b7 100644
--- a/content/common/site_isolation_policy.h
+++ b/content/common/site_isolation_policy.h
@@ -41,12 +41,6 @@ class CONTENT_EXPORT SiteIsolationPolicy {
   // different process from the main frame.
   static bool IsTopDocumentIsolationEnabled();
 
-  // Returns true if navigation and history code should maintain per-frame
-  // navigation entries. This is an in-progress feature related to site
-  // isolation, so the return value is currently tied to --site-per-process.
-  // TODO(creis, avi): Make this the default, and eliminate this.
-  static bool UseSubframeNavigationEntries();
-
  private:
   SiteIsolationPolicy();  // Not instantiable.