refactor(perf): e2e tests and benchpress should be written in es6

tools/benchpress/index.es6

@@ -1,5 +1,5 @@
-var timeBenchmark = require('./time_benchmark');
-var tools = require('./tools');
+var timeBenchmark = require('./src/time_benchmark');
+var tools = require('./src/tools');
 
 module.exports = {
   runTimeBenchmark: timeBenchmark.runTimeBenchmark,

tools/build/benchpress.js

@@ -0,0 +1,6 @@
+module.exports = function(gulp, plugins, config) {
+  return function(done) {
+    del(config.path, done);
+  };
+};
+