Add notifications to allow desktop notification permissions to be synced.

base/values.h

Index: base/values.h
diff --git a/base/values.h b/base/values.h
index 6c66345b5791b37a4e6e6fdbda45d4a5b9016d6d..248fc1d6e9d65620cd32d797964b91bb340b2f95 100644
--- a/base/values.h
+++ b/base/values.h
@@ -401,6 +401,10 @@ class ListValue : public Value {
   // Appends a Value to the end of the list.
   void Append(Value* in_value);
 
+  // Appends a Value if it's not already present.
+  // Returns true if successful, or false if the value was already present.
+  bool AppendIfNotPresent(Value* in_value);
+
   // Insert a Value at index.
   // Returns true if successful, or false if the index was out of range.
   bool Insert(size_t index, Value* in_value);