power_LoadTest: Add parameter for custom tasks

client/site_tests/power_LoadTest/extension/params.js

Index: client/site_tests/power_LoadTest/extension/params.js
diff --git a/client/site_tests/power_LoadTest/extension/params.js b/client/site_tests/power_LoadTest/extension/params.js
index dca948790f0bafe5d817959d760a774e21f9d9f8..9df4d07696081e8e25f7ddd834671e9456f2f9fd 100644
--- a/client/site_tests/power_LoadTest/extension/params.js
+++ b/client/site_tests/power_LoadTest/extension/params.js
@@ -2,8 +2,18 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-var test_time_ms = 60 * 60 * 1000;
-var test_startup_delay = 5 * 1000;
+// Convert seconds to milliseconds
+function seconds(s) {
+    return s * 1000;
+}
+
+// Convert minutes to milliseconds
+function minutes(m) {
+    return seconds(m * 60);
+}
+
+var test_time_ms = minutes(60);
+var test_startup_delay = seconds(5);
 var should_scroll = true;
 var should_scroll_up = true;
 var scroll_loop = false;