As of now, Google Chrome BETA does not support themes officially and provides no way to manage them, However, free software are now available to easily create, install and manage themes for the browser

Xchrome Theme Manager is the first and only software currently available to install and manage Google Chrome Themes, The free software is still in BETA but lets you fully automate the installation of Google Chrome themes without any hassles

Xchrome Theme Manager Features

Automated Theme Installation
Edit and build your own Google Chrome themes
List of all Google Chrome installed Theme with preview and author details
Theme Installer for creating single click Google Chrome theme installers