setup for perf testing yui loader

setup.js

function getTime () {
    return new Date().getTime();
}

function patchLoader (Y, loader) {
    var YUI     = Y.config.global.YUI,
        seq     = 0,
        methods,
        current,
        perf,
        orig,
        len,
        i;

    perf = YUI.Env.perf = {
        YUI_start: Y.config.YUI_start,
        first_Get: null,
        YUI_instantiation_to_first_Get: null
    };
    perf.instantiation = {};

    // Generic way to instrument a function. Uses sequencing to support
    // multiple invocations during a single `Y.use()` call.
    function instrument (obj, name) {
        var orig = obj[name];

        obj[name] = function () {
            var now = getTime(),
                key = name + '__' + seq++,
                contextTimers,
                methodTimers,
                value;

            // If a `use` statement isn't in the current stack, then its timer
            // obj isn't available. Use the instantiation timer obj instead.
            contextTimers = current || perf.instantiation;

            // Initialize the method count object
            contextTimers.count = contextTimers.count || {};

            // Initialize the time object for the currently instrumented method
            methodTimers = contextTimers[key] = {};

            methodTimers.start = now;
            value = orig.apply(obj, arguments);
            methodTimers.end = getTime();
            methodTimers.duration = methodTimers.end - methodTimers.start;

            contextTimers.count[name] = contextTimers.count[name] || 0;
            contextTimers.count[name] += 1;
            
            return value;
        };
    }

    orig = {
        YGetjs:  Y.Get.js,
        Y_use:   Y._use
    };

    // Start of the `Y.use()` invocation
    Y._use = function () {
        var now = getTime(),
            useId;

        // unique id for current `use` invocation
        useId = '_use__' + arguments[0].join(',') + '__' + now;

        current = perf[useId] = {
            start: now,
            end: null,
            duration: null
        };
        orig.Y_use.apply(Y, arguments);
    };

    // Effective end of the `Y.use()` invocation before things get async
    Y.Get.js = function () {
        var now = getTime();

        current.end = now;
        current.duration = current.end - current.start;
        
        if (!perf.first_Get) {
            perf.first_Get = now;
            perf.YUI_instantiation_to_first_Get = perf.first_Get - perf.YUI_start;
        }

        return orig.YGetjs.apply(Y.Get, arguments);
    };

    methods = [
        '_setup',
        '_rollup',
        '_sort',
        '_explode',
        'addModule',
        'calculate'
    ];

    for (i = 0, len = methods.length; i < len; i += 1) {
        instrument(loader, methods[i]);
    }
}

YUI_config = window.YUI_config || {};
YUI_config.YUI_start = getTime();
YUI_config.hookForLoader = patchLoader;