Remove PersistentPrefStore::MarkNeedsEmptyValue.

base/values.h

Index: base/values.h
diff --git a/base/values.h b/base/values.h
index bb23ffc2e31bc7b4ca2b2e2c36653534f1389355..52b2a2472f69fdf64a6fab4139029812f4b808e1 100644
--- a/base/values.h
+++ b/base/values.h
@@ -322,6 +322,10 @@ class BASE_EXPORT DictionaryValue : public Value {
   virtual bool RemoveWithoutPathExpansion(const std::string& key,
                                           Value** out_value);
 
+  // Removes a path, clearing out all dictionaries on |path| that remain empty
+  // after removing the value at |path|.
+  virtual bool RemovePath(const std::string& path, Value** out_value);
+
   // Makes a copy of |this| but doesn't include empty dictionaries and lists in
   // the copy.  This never returns NULL, even if |this| itself is empty.
   DictionaryValue* DeepCopyWithoutEmptyChildren();