Add TODO to refactor error handling. (flutter#131878)

Author: polina-c

packages/flutter/lib/src/foundation/stack_frame.dart

@@ -78,6 +78,9 @@ class StackFrame {
         // On the Web in non-debug builds the stack trace includes the exception
         // message that precedes the stack trace itself. fromStackTraceLine will
         // return null in that case. We will skip it here.
+        // TODO(polina-c): if one of lines was parsed to null, the entire stack trace
+        // is in unexpected format and should be returned as is, without partial parsing.
+        // https://github.com/flutter/flutter/issues/131877
         .whereType<StackFrame>()
         .toList();
   }