So, revid:<email address hidden> merged revid:<email address hidden> .
In the ancestry of the later, there is revid:<email address hidden> which modifies storage/innodb_plugin/ChangeLog and since this revisions is not part of the 5.5 history, this generates a content conflict since 5.5 deleted the Changelog and 5.1 modified it since the last merge from 5.1
So, revid:<email address hidden> merged revid:<email address hidden> .
In the ancestry of the later, there is revid:<email address hidden> which modifies storage/ innodb_ plugin/ ChangeLog and since this revisions is not part of the 5.5 history, this generates a content conflict since 5.5 deleted the Changelog and 5.1 modified it since the last merge from 5.1