Read this- http://www.chromium.org/developers/how-tos/get-the-code
You have to install the required tools to read the source code on Windows.
Linux and Mac already have the required tools installed to read the source code.
Stable source code releases can have different build numbers on each platform. (Windows, Mac OS X, Linux, Android and iOS)
But you can use any platform to build Chromium for other platforms.
I'm not 100% sure but I have read that Google uses Mac OS X to build Chrome for all of their platform versions. Of coarse it would make sense since Chromium was developed from Apple Webkit.
The stable Chromium source code usually has the same build numbers of the stable releases of Google Chrome. However third-party developers may choose to use their own build numbers independent from the source code releases. (SRWare Iron, CoolNovo, Comodo Dragon, Superbird, BlackHawk Web Browser, Yandex Browser, RockMelt, Torch Browser, etc.)
Thanks.