gistfile1.js

(function() {

// ==UserScript==
// @name      Google Code Search Improver
//
// @include   http://google.com/codesearch/*
// @include   http://www.google.com/codesearch/*
// @include   https://google.com/codesearch/*
// @include   https://www.google.com/codesearch/*
//
// ==/UserScript==

var top_bar     = document.getElementsByClassName("GOYGFLXBJQ")[0],
    content_div = top_bar.parentNode.nextSibling;

var toggle_top_bar = function(evt) {
    if (evt.keyCode === 85) {
        top_bar.style.display = (top_bar.style.display === "none" ? "" : "none");
        content_div.style.top = (content_div.style.top === "0px" ? "85px" : "0px");
    }
};

document.body.addEventListener("keydown", toggle_top_bar, false);    

})();