Persist sessionStorage on disk.

content/public/browser/dom_storage_context.h

Index: content/public/browser/dom_storage_context.h
diff --git a/content/public/browser/dom_storage_context.h b/content/public/browser/dom_storage_context.h
index 99f8cd142e883dea54a970d99baf227d78414cda..782663308150843f9684831102d756014b1d6329 100644
--- a/content/public/browser/dom_storage_context.h
+++ b/content/public/browser/dom_storage_context.h
@@ -31,6 +31,12 @@ class DOMStorageContext {
   // Deletes the local storage data for the given origin.
   virtual void DeleteOrigin(const GURL& origin) = 0;
 
+  // If this is called, sessionStorage data will be stored on disk, and can be
+  // restored after a browser restart (with RecreateSessionStorage). This
+  // function must be called right after DOMStorageContextImpl is created, and
+  // before it's used.
+  virtual void SetSaveSessionStorageOnDisk() = 0;
+
   // Creates a SessionStorageNamespace with the given |persistent_id|. Used
   // after tabs are restored by session restore. When created, the
   // SessionStorageNamespace with the correct |persistent_id| will be
@@ -38,6 +44,11 @@ class DOMStorageContext {
   virtual scoped_refptr<SessionStorageNamespace> RecreateSessionStorage(
       const std::string& persistent_id) = 0;
 
+  // Starts deleting sessionStorages which don't have an associated
+  // SessionStorageNamespace alive. Called when SessionStorageNamespaces have
+  // been created after a session restore, or a session restore won't happen.
+  virtual void StartScavengingUnusedSessionStorage() = 0;
+
  protected:
   virtual ~DOMStorageContext() {}
 };