overrideMimeType should be called after open to be spec compliant

chrome/test/data/extensions/subscribe_page_action/subscribe.js

Index: chrome/test/data/extensions/subscribe_page_action/subscribe.js
diff --git a/chrome/test/data/extensions/subscribe_page_action/subscribe.js b/chrome/test/data/extensions/subscribe_page_action/subscribe.js
index 65593c6fb8960c29989b0bd7f5abdda92f8c3b31..acf9d0edf2077135fd90d881cdb1fe325a78580c 100644
--- a/chrome/test/data/extensions/subscribe_page_action/subscribe.js
+++ b/chrome/test/data/extensions/subscribe_page_action/subscribe.js
@@ -127,11 +127,11 @@ function main() {
 
   req.onload = handleResponse;
   req.onerror = handleError;
+  req.open("GET", feedUrl, !synchronousRequest);
   // Not everyone sets the mime type correctly, which causes handleResponse
   // to fail to XML parse the response text from the server. By forcing
   // it to text/xml we avoid this.
   req.overrideMimeType('text/xml');
-  req.open("GET", feedUrl, !synchronousRequest);
   req.send(null);
 
   document.getElementById('feedUrl').href = 'view-source:' + feedUrl;