How can I add a custom search engine to Chrome (beta, stable...)? Call me dumb, but, I don't see an obvious way to do this. 

I want to add duckduckgo.com as the main search engine in Google Chrome for Android (beta, stable...)
As of chrome v39, this still can't easily be done; however, you can hack it. From  the XDA post SomeNickName referenced:


Install a Terminal emulator or use adb shell if you're familiar with it.
Change the "last_known_google_url" and "last_prompted_google_url" settings support having a search&amp;q=added to the end. For example, duckduckgo would work with, https://www.duckduckgo.com&amp; -- where the extra ampersand at the end is for converting the "search" text into an additional query sting param.


Here's a shell command for setting the duckduckgo url:

    p='/data/data/com.chrome.beta/app_chrome/Default/Preferences'
    awk '/last_known_google_url/ {sub(/google.com\//,"duckduckgo.com/\\&amp;")}; {print}' ${p} &gt; $p.bak
    awk '/last_prompted_google_url/ {sub(/google.com\//,"duckduckgo.com/\\&amp;")}; {print}' ${p}.bak &gt; ${p}