chore(util): add requestIdleCallback polyfill

src/util/test/util.spec.ts

@@ -340,4 +340,12 @@ describe('util', () => {
 
   });
 
+  describe('requestIdleCallback polyfill', () => {
+
+    it('should return a value lazily', () => {
+      expect(util.requestIonicCallback(() => { return 1; })).toEqual(1);
+    });
+
+  });
+
 });

src/util/util.ts

@@ -179,6 +179,15 @@ function _assert(actual: any, reason: string) {
   }
 }
 
+/** @private */
+export function requestIonicCallback(functionToLazy: any) {
+  if ('requestIdleCallback' in window) {
+    return (window as any).requestIdleCallback(functionToLazy);
+  } else {
+    return setTimeout(functionToLazy, 500);
+  }
+}
+
 /** @private */
 export { _assert as assert};