Persist sessionStorage on disk.

chrome/browser/ui/startup/startup_browser_creator_impl.cc

Index: chrome/browser/ui/startup/startup_browser_creator_impl.cc
diff --git a/chrome/browser/ui/startup/startup_browser_creator_impl.cc b/chrome/browser/ui/startup/startup_browser_creator_impl.cc
index a6a09e89bc733940ecffef1f92fa44c9dd3dce59..b148c24a7c5687cbee10a07f8d85e8690779008c 100644
--- a/chrome/browser/ui/startup/startup_browser_creator_impl.cc
+++ b/chrome/browser/ui/startup/startup_browser_creator_impl.cc
@@ -72,6 +72,7 @@
 #include "chrome/common/url_constants.h"
 #include "chrome/installer/util/browser_distribution.h"
 #include "content/public/browser/child_process_security_policy.h"
+#include "content/public/browser/dom_storage_context.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 #include "content/public/browser/web_contents.h"
@@ -619,6 +620,17 @@ bool StartupBrowserCreatorImpl::ProcessStartupURLs(
     return false;
 
   AddInfoBarsIfNecessary(browser, chrome::startup::IS_PROCESS_STARTUP);
+
+  // Session restore may occur if the startup preference is "last" or if the
+  // crash infobar is displayed. Otherwise, it's safe for the DOM storage system
+  // to start deleting leftover data.
+  if (pref.type != SessionStartupPref::LAST &&
+      !HasPendingUncleanExit(profile_)) {
+    content::DOMStorageContext* dom_storage_context =
+        content::BrowserContext::GetDOMStorageContext(profile_);
+    dom_storage_context->StartScavengingUnusedSessionStorage();
+  }
+
   return true;
 }