Right-click a column of text and pick "Zoom" to make it take up the whole width of the screen. Esc unzooms.
Or you can tap Shift then click a column of text to zoom in on it, and/or press +/-/0 to adjust the font size. If you tap Shift accidentally, cancel zooming by tapping it again (or pressing any other key).
This extension works best for text-heavy sites: news, blogs, and so forth. It won't zoom all content correctly, and it's disabled for some sites like GMail and Hotmail where it doesn't work. Like all extensions, it's disabled on this site, too. And it's experimental: it could cause you problems.
If the keyboard shortcuts interfere with a webpage, you can disable them on a page by pressing ` (the backquote key, underneath Escape on some keyboards).
If you like this extension, take a look at the Readability Redux extension (by different folks), which lets you strip many news/blog sites down to plain text.
Note: This extension was originally published by another author. I loved this extension but it was not maintained any more and it was not worked on recent version of chrome. So I decided to fix it for latest chrome. I really appreciate original authors' efforts.