PasteTab/src/scripts/background.js

var result = '';

function getContentFromClipboard() {
    var sandbox = document.getElementById('sandbox');
    sandbox.value = '';
    sandbox.select();
    if (document.execCommand('paste'))
	result = sandbox.value;
    chrome.browserAction.setBadgeText({text: result.length.toString() });
    return result;
}

function onClickHandler() {
    window.open().document.write('<pre>' + getContentFromClipboard() + '</pre>');
}

chrome.runtime.onMessage.addListener(function (request, sender, sendResponse) {
    if (request.event == 'copy') getContentFromClipboard();
});

chrome.browserAction.setBadgeText({ text: '' });
chrome.browserAction.onClicked.addListener(onClickHandler);