Explicitly CHECK arguments in dbus::MessageWriter::AppendString/ObjectPath

dbus/object_path.h

Index: dbus/object_path.h
diff --git a/dbus/object_path.h b/dbus/object_path.h
index 59071daa6e5540d33c36659f0ae98a45f785ff9a..38e1fe2cca536434b92acfaa0fb83ffe729e8a6c 100644
--- a/dbus/object_path.h
+++ b/dbus/object_path.h
@@ -29,6 +29,9 @@ class ObjectPath {
   // Retrieves value as a std::string.
   const std::string& value() const { return value_; }
 
+  // Returns true if the value is a valid object path.
+  bool IsValid() const;
+
   // Permit sufficient comparison to allow an ObjectPath to be used as a
   // key in a std::map.
   bool operator<(const ObjectPath&) const;