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

chrome/browser/value_store/testing_value_store.h

Index: chrome/browser/value_store/testing_value_store.h
diff --git a/chrome/browser/value_store/testing_value_store.h b/chrome/browser/value_store/testing_value_store.h
index 53fc7c81f1c3c7645b1f85597b69919a122066e6..c3847407025695cea0672a85d6084cc36402a31c 100644
--- a/chrome/browser/value_store/testing_value_store.h
+++ b/chrome/browser/value_store/testing_value_store.h
@@ -43,6 +43,10 @@ class TestingValueStore : public ValueStore {
   virtual WriteResult Remove(const std::string& key) OVERRIDE;
   virtual WriteResult Remove(const std::vector<std::string>& keys) OVERRIDE;
   virtual WriteResult Clear() OVERRIDE;
+  // TestingValueStores can't get corrupted (they're all in-memory), so these
+  // just return true.
+  virtual bool Restore() OVERRIDE;
+  virtual bool RestoreKey(const std::string& key) OVERRIDE;
 
  private:
   scoped_ptr<ValueStore::Error> TestingError();