Fix errors reported by the space-infix-ops ESLint rule

http://eslint.org/docs/rules/space-infix-ops

extensions/chromium/pdfHandler.js

@@ -54,7 +54,7 @@ function isPdfDownloadable(details) {
  * @return {undefined|{name: string, value: string}} The header, if found.
  */
 function getHeaderFromHeaders(headers, headerName) {
-  for (var i=0; i<headers.length; ++i) {
+  for (var i = 0; i < headers.length; ++i) {
     var header = headers[i];
     if (header.name.toLowerCase() === headerName) {
       return header;