Chromium is an open source web browser that was designed in order to provide for all users a safer, faster, and more stable way to experience the web. In the long term, we think of Chromium as a tabbed window manager or shell for the web rather than a browser application. We avoid putting things into our UI in the same way you would hope that Apple and Microsoft would avoid putting things into the standard window frames of applications on their operating systems.

The tab is our equivalent of a desktop application's title bar; the frame containing the tabs is a convenient mechanism for managing groups of those applications. In future, there may be other tab types that do not host the normal browser toolbar.

Enhanced functionality through HTML 5: offline modes, background processing, notifications, and more.
Better access points and discovery: On Chromium-based browsers, we've addressed the access point issue by allowing applications to install shortcuts on your desktop.

While the tab bar is sufficient to access existing tabs, we are creating a new primary access point that provides a list of frequently used applications and tools.
Search as a primary form of navigation
Chromium's address bar and the Quick Search Box have simplified the way you access personal content and the web.

While we're not a natively-themed application, we do wish to fit within the operating system so that our app doesn't look out of place. This affects our choices of:

interface icons
color
perceived depth, thickness
border shape, width and styling
font choice
blurriness - Windows tends to be more bitmappy than OS X, preferring to align everything along pixel boundaries