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 236b0b82230db90f1026ea304e7d386741f6da73..5c0705b97bec556100dbf84b3423595d61797ab1 100644
--- a/chrome/browser/ui/startup/startup_browser_creator_impl.cc
+++ b/chrome/browser/ui/startup/startup_browser_creator_impl.cc
@@ -68,7 +68,9 @@
 #include "chrome/common/pref_names.h"
 #include "chrome/common/url_constants.h"
 #include "chrome/installer/util/browser_distribution.h"
+#include "content/public/browser/browser_context.h"
 #include "content/public/browser/child_process_security_policy.h"
+#include "content/public/browser/dom_storage_context.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/browser/web_contents_view.h"
 #include "grit/locale_settings.h"
@@ -563,6 +565,17 @@ bool StartupBrowserCreatorImpl::ProcessStartupURLs(
     return false;
 
   AddInfoBarsIfNecessary(browser, browser::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;
 }