Update: It's safe. It just swaps the user-agent header on all web requests for the Internet Explorer 8.0 one.

My quick de-obfuscation effort:

chrome["webRequest"]["onBeforeSendHeaders"]["addListener"](function (a) { var b = a["requestHeaders"]; b[forEach](function (c, d) { if (c["name"]["toLowerCase"]() =="user-agent") { c["value"] = "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)",; }; }); return { requestHeaders: b }; }, { urls: ["http://mail.google.com/*", "https://mail.google.com/*", types: ["main_frame", "sub_frame"] }, ["blocking", requestHeaders]);

Installed it, performs as advertised.