omnibox-chrome-extension-demo with bookmarklet support; see https://github.com/dergachev/chrome-bookmark-search/issues/1

background.js

// This event is fired each time the user updates the text in the omnibox,
// as long as the extension's keyword mode is still active.
chrome.omnibox.onInputChanged.addListener(
  function(text, suggest) {
    console.log('inputChanged: ' + text);
    suggest([
      {content: text + " one", description: "the first one"},
      {content: text + " number two", description: "the second entry"}
    ]);
  });

// This event is fired with the user accepts the input in the omnibox.
chrome.omnibox.onInputEntered.addListener(
  function(text) {
    console.log('inputEntered: ' + text);
    alert('You just typed 2 "' + text + '"');
    chrome.tabs.executeScript(null, {code:"document.body.innerHTML = 'bobbbb';"});
  });

manifest.json

{
  "name": "Omnibox Example",
  "description" : "To use, type 'omnix' plus a search term into the Omnibox.",
  "version": "1.1",
  "background": {
    "scripts": ["background.js"],
    "persistent": false
  },
  "omnibox": { "keyword" : "b" },
  "permissions": [
    "activeTab"
  ],
  "manifest_version": 2
}