Open up your settings in Chrome and go to "Manage search engines...". Check to see if imdb is listed under "Default search settings". If it is, hover on it and click the X all the way over on the right. This should remove imdb from the list. If it is not listed under "Default search settings", see if it is listed under "Other search engines" down the page a bit. Again, remove imdb from this list if it is there.
Now, open up a new tab and go to imdb. Search anything in the usual way you would when visiting the site. Now go back to "Manage search engines". Imdb should show up under "Other search engines". Hover on it, and click "Make default". You've now enabled imdb as a shortcut, and it should have moved itself from "Other search engines" to "Default search settings" (the top one). The middle column should read "imdb.com". This is what you type into Chrome's omnibox (the address bar in chrome). Type "imdb.com" and hit tab and enter what you want to search for.
I prefer this method to trying to find or guess the search string because that is often version-specific.
For reference, I am using version: 29.0.1547.65 of Chrome
Note: Following the previous steps may make imdb your primary search engine (typing anything in the omnibox will search imdb) while also creating a shortcut. If you want to revert back to your favorite primary search engine, go to Settings -> Search, and change the value of the dropdown from IMDb back to whatever it was. Imdb should still be a shortcut.