feat(bench press): use chrome tracing protocol and initial iOS support

modules/benchpress/benchpress.js

@@ -10,6 +10,7 @@ export { ConsoleReporter } from './src/reporter/console_reporter';
 export { SampleDescription } from './src/sample_description';
 export { PerflogMetric } from './src/metric/perflog_metric';
 export { ChromeDriverExtension } from './src/webdriver/chrome_driver_extension';
+export { IOsDriverExtension } from './src/webdriver/ios_driver_extension';
 export { Runner } from './src/runner';
 export { Options } from './src/sample_options';
 export { MeasureValues } from './src/measure_values';