Persist sessionStorage on disk.

chrome/browser/sessions/session_restore.cc

Index: chrome/browser/sessions/session_restore.cc
diff --git a/chrome/browser/sessions/session_restore.cc b/chrome/browser/sessions/session_restore.cc
index 2e7e489bd80dd5d776df6d41eb8b77a4acc99323..732643dd808077eb4cc947f04ac6f5dd65354c35 100644
--- a/chrome/browser/sessions/session_restore.cc
+++ b/chrome/browser/sessions/session_restore.cc
@@ -824,6 +824,13 @@ class SessionRestoreImpl : public content::NotificationObserver {
     Browser* finished_browser = FinishedTabCreation(true, has_tabbed_browser);
     if (finished_browser)
       last_browser = finished_browser;
+
+    // sessionStorages needed for the session restore have now been recreated
+    // by RestoreTab. Now it's safe for the DOM storage system to start
+    // deleting leftover data.
+    content::DOMStorageContext* dom_storage_context =
+        content::BrowserContext::GetDOMStorageContext(profile_);
+    dom_storage_context->StartScavengingUnusedSessionStorage();
     return last_browser;
   }