Mojo: Report bindings validation errors via MojoNotifyBadMessage

mojo/public/cpp/bindings/lib/message_header_validator.h

Index: mojo/public/cpp/bindings/lib/message_header_validator.h
diff --git a/mojo/public/cpp/bindings/lib/message_header_validator.h b/mojo/public/cpp/bindings/lib/message_header_validator.h
index bccef1f772a4cfa6184dff3b924f497c23c90cdc..6e56b7f0ad92217dd9333f9c519f4516c1ccc3ac 100644
--- a/mojo/public/cpp/bindings/lib/message_header_validator.h
+++ b/mojo/public/cpp/bindings/lib/message_header_validator.h
@@ -14,8 +14,17 @@ namespace internal {
 class MessageHeaderValidator : public MessageFilter {
  public:
   explicit MessageHeaderValidator(MessageReceiver* sink = nullptr);
+  MessageHeaderValidator(const std::string& description,
+                         MessageReceiver* sink = nullptr);
+
+  // Sets the description associated with this validator. Used for reporting
+  // more detailed validation errors.
+  void SetDescription(const std::string& description);
 
   bool Accept(Message* message) override;
+
+ private:
+  std::string description_;
 };
 
 }  // namespace internal