Add ownership semantic comments to error.h

src/core/lib/iomgr/error.h

@@ -165,6 +165,8 @@ void grpc_error_unref(grpc_error* err);
 grpc_error* grpc_error_set_int(grpc_error* src, grpc_error_ints which,
                                intptr_t value) GRPC_MUST_USE_RESULT;
 bool grpc_error_get_int(grpc_error* error, grpc_error_ints which, intptr_t* p);
+/// This call takes ownership of the slice; the error is responsible for
+/// eventually unref-ing it.
 grpc_error* grpc_error_set_str(grpc_error* src, grpc_error_strs which,
                                grpc_slice str) GRPC_MUST_USE_RESULT;
 /// Returns false if the specified string is not set.
@@ -174,7 +176,8 @@ bool grpc_error_get_str(grpc_error* error, grpc_error_strs which,
 
 /// Add a child error: an error that is believed to have contributed to this
 /// error occurring. Allows root causing high level errors from lower level
-/// errors that contributed to them.
+/// errors that contributed to them. The src error takes ownership of the
+/// child error.
 grpc_error* grpc_error_add_child(grpc_error* src,
                                  grpc_error* child) GRPC_MUST_USE_RESULT;
 grpc_error* grpc_os_error(const char* file, int line, int err,