AOL CEO Tim Armstrong told the Wall Street Journal at Cannes Lions that the topic of Google's and Facebook's growing online dominance has "loomed over many conversations" in the past week, coming up at nearly every meeting with publishers and advertisers he's taken. Armstrong said the concern centers on walled-garden strategies. Facebook and Google are increasingly restricting third-party companies from operating on their networks and from accessing their data, he told the WSJ. That will prompt AOL to pursue more open strategies.