Thankfully, there's an app for that! Chrome Toolbox will allow you to double click any tab to close it.
Download it here and press the "+ add to chrome" button.
After it is installed, you can go into Chrome Toolbox's options and tick "Double click on a tab to close it". Settings are saved automatically.
Chrome Toolbox also comes with a ton of other nifty features:
- Magnify any image on a web page, set it as your wallpaper, and view it in its original size
- Drag any video on a web page (Flash and HTML5 video) out of the page in its own stand--alone window, closing the window puts it back to the original page, both with play state reservation
- Customize tab behavior to close the tab on double click, to create a new tab on closing the last tab, and to always open a link in its own tab
- Save and restore unsubmitted form data, to avoid data loss caused by session expiration or a no-cache page setting
- One shortcut to launch all predefined URLs (from your Bookmark Manager folder)
- Learn, compare and contrast shortcuts in Chrome and other popular browsers.
- Put your favorite Chrome functionalities in the drop down menu, reorder them in the way you like
- Define Boss Key
- Mute all tabs