fixup! test(mdc-checkbox): add performance tests for mdc-checkbox

Author: wagnermaciel

test/benchmarks/mdc/checkbox/app.module.ts

@@ -29,6 +29,10 @@ import {MatCheckboxModule} from '@angular/material-experimental/mdc-checkbox';
   styleUrls: ['//src/material-experimental/mdc-theming/prebuilt/indigo-pink.css'],
 })
 export class CheckboxBenchmarkApp {
+
+  // isChecked is used to maintain the buttons checked state even after it has been hidden. This is
+  // used, for example, when we want to test the render speed of a checked vs unchecked checkbox.
+
   isChecked = false;
   isVisible = false;
   isIndeterminate = false;