Add missing shortcut keys to the keyboard overlay.

This CL adds the following shortcuts to the keyboard overlay.

* Alt - 1, Alt - 2, .., Alt - 8: go to the window at the specified position
* Alt - 9: go to the last window open
* Ctrl - Forward: switches focus to the next keyboard-accessible pane
* Ctrl - Back: switches focus to the previous keyboard-accessible pane
* Ctrl - Right: move the text cursor to the end of the next word
* Ctrl - Left: move the text cursor to the start of the previous word
* Ctrl - Alt - Z: enable or disable accessibility features
* Ctrl - Shift - Maximize: take a screenshot of the selected region
* Ctrl - Shift - O: open the Bookmark Manager

I also deleted a duplicated entry of "Close window".


BUG=chromium-os:17152
TEST=Manually checked on chromebook


Review URL: http://codereview.chromium.org/7489040

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@93906 0039d316-1c4b-4281-b951-d872f2087c98
  virtual std::string GetMimeType(const std::string&) const {
    return "text/html";
  }

  virtual std::string GetMimeType(const std::string&) const {
    return "text/html";
  }
