Chrome used to show a dialog that asked you to pick your favorite search engine when you installed the browser. Now it no longer does this and Google is the default search engine. Anyway, it's likely that Google is the default search engine for most Chrome users.
I clicked "Show me how" and Google sent me to this page with instructions that explained how to change the search provider to Google and how to change the homepage to Google.
Google has similar pages for Firefox, Safari, Opera and Internet Explorer. In most countries, the default search engine for Firefox, Safari and Opera is Google, so it's strange to see this campaign.