@Override
    public boolean isValidContext(ActionContext context) {
        return (context.getContextObject() instanceof FieldHeaderLocation);
    }
Constructor takes the CodeBrowserPlugin that created it and the header
component so that it can be repainted when fields are added.
@param owner the action owner	
@param panel the listing panel.
Ghidra/Features/Base/src/main/java/ghidra/app/util/viewer/format/actions/AddAllFieldAction.java