Remove JsonPrefStore pruning of empty values on write.

base/prefs/pref_service.h

Index: base/prefs/pref_service.h
diff --git a/base/prefs/pref_service.h b/base/prefs/pref_service.h
index ae61e40e0a5a95a35056c48ff80658691be97668..e7b8914071ec59fe704dfca6be930d01a402e200 100644
--- a/base/prefs/pref_service.h
+++ b/base/prefs/pref_service.h
@@ -221,13 +221,6 @@ class BASE_PREFS_EXPORT PrefService : public base::NonThreadSafe {
   // registered preference. In that case, will never return NULL.
   const base::Value* GetDefaultPrefValue(const char* path) const;
 
-  // Deprecated. Do not add calls to this method.
-  // Marks that the user store should not prune out empty values for |key| when
-  // writting to disk.
-  // TODO(gab): Enforce this at a lower level for all values and remove this
-  // method.
-  void MarkUserStoreNeedsEmptyValue(const std::string& key) const;
-
   // Returns true if a value has been set for the specified path.
   // NOTE: this is NOT the same as FindPreference. In particular
   // FindPreference returns whether RegisterXXX has been invoked, where as