Add a Restore() method to ValueStore and make StorageAPI use it

chrome/browser/extensions/api/storage/policy_value_store.h

Index: chrome/browser/extensions/api/storage/policy_value_store.h
diff --git a/chrome/browser/extensions/api/storage/policy_value_store.h b/chrome/browser/extensions/api/storage/policy_value_store.h
index f32d30740b7b59bd0f4688c2bbafdf1af17c0958..70ed25229bfdaf670602d9118bd378eaadcaf995 100644
--- a/chrome/browser/extensions/api/storage/policy_value_store.h
+++ b/chrome/browser/extensions/api/storage/policy_value_store.h
@@ -55,6 +55,9 @@ class PolicyValueStore : public ValueStore {
   virtual WriteResult Remove(const std::string& key) OVERRIDE;
   virtual WriteResult Remove(const std::vector<std::string>& keys) OVERRIDE;
   virtual WriteResult Clear() OVERRIDE;
+  // Hopefully, as a Read-Only database, there is no reason to use these.
+  virtual bool Restore() OVERRIDE;
+  virtual bool RestoreKey(const std::string& key) OVERRIDE;
 
   // For unit tests.
   ValueStore* delegate() { return delegate_.get(); }