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 98708651d0277a09c6280b2421149f3345f1250c..43b9aacedfd32543d26918e40688129de177fa4f 100644
--- a/chrome/browser/sessions/session_restore.cc
+++ b/chrome/browser/sessions/session_restore.cc
@@ -732,7 +732,11 @@ class SessionRestoreImpl : public content::NotificationObserver {
         100);
 
     if (windows->empty()) {
-      // Restore was unsuccessful.
+      // Restore was unsuccessful. The DOM storage system can also delete its
+      // data, since no session restore will happen at a later point in time.
+      content::DOMStorageContext* dom_storage_context =
+          content::BrowserContext::GetDOMStorageContext(profile_);
+      dom_storage_context->StartScavengingUnusedSessionStorage();
       return FinishedTabCreation(false, false);
     }
 
@@ -821,6 +825,13 @@ 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;
   }