Check if the window.performance should be used in a duck-typy way

In my Rollup setup, there is a fake `global` object that is a reference to `window`, which means that the polyfill (meant for Node.js) will be used instead of `window.performance`.
I'd rather check if `window` exists and has a `performance()` method, and then only use the polyfill if it's not the case.

Author: getkey

src/performance.js

@@ -5,7 +5,7 @@ let perf = null, start = Date.now();
 
 // use global browser performance module
 // for node create a polyfill
-if (!global) {
+if (typeof window !== 'undefined' && window.performance) {
   perf = window.performance;
 } else {
   perf = {
@@ -15,4 +15,4 @@ if (!global) {
   };
 }
 
-export default perf;
+export default perf;