As detailed in the documentation you cannot use chrome.* API within content scripts except for some chrome.extension.* methods.

However, this doesn't really limit you as you can use messaging to call your content script from your background page. For example;

background.html

<script type="application/javascript">
chrome.browserAction.onClicked.addListener(function() {
    chrome.tabs.getSelected(function (tab) {
        chrome.tabs.sendRequest(tab.id, {title: 'new page title'}, function (response) {});
    });
});
</script>

changetitle.js

chrome.extension.onRequest.addListener(function (request, sender, sendResponse) {
    document.title = request.title;
});

You will of course require the tabs permission in order to use this technique.