resolves #204 - pull request to add reporting advice for incorrect mi…

…me type headers

lib/har/performance/mimeTypes.js

@@ -0,0 +1,23 @@
+'use strict';
+module.exports = {
+  id: 'mimeTypes',
+  title: 'Avoid using incorrect mime types',
+  description: 'It\'s not a great idea to let browsers guess content types (content sniffing), in some cases it can actually be a security risk.',
+  weight: 0,
+  tags: ['performance', 'bestpractice'],
+  processPage: function(page) {
+    let score = 100;
+    let offending = [];
+    page.assets.forEach(function(asset) {
+        if (asset.type == "other" && (asset.status >199 && asset.status < 300)) {
+            score--;
+            offending.push(asset.url);
+        }
+    });
+    return {
+      score: Math.max(0, score),
+      offending: offending,
+      advice: score < 100 ? 'The page has ' + offending.length + ' misconfigured mime type(s). ' : ''
+    };
+  }
+};