Added tracking of order of types declared.

Change-Id: Iade313c99f119dcf1619674260648a33f61dc030

include/flatbuffers/idl.h

@@ -578,6 +578,7 @@ private:
                                        BaseType baseType);
 
  public:
+  SymbolTable<Type> types_;
   SymbolTable<StructDef> structs_;
   SymbolTable<EnumDef> enums_;
   SymbolTable<ServiceDef> services_;